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Wikipedia

Water

February 15, 2023

For other uses, see Water (disambiguation).
"H2O" and "H20" redirect here. For other uses, see H20 (disambiguation) and H₂O (disambiguation).

Water is an inorganic compound with the chemical formula H2O. It is a transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a solvent[1]). It is vital for all known forms of life, despite not providing food, energy or organic micronutrients. Its chemical formula, H2O, indicates that each of its molecules contains one oxygen and two hydrogen atoms, connected by covalent bonds. The hydrogen atoms are attached to the oxygen atom at an angle of 104.45°.[2] "Water" is also the name of the liquid state of H2O at standard temperature and pressure.

Water
Names
IUPAC name
Water
Systematic IUPAC name
Oxidane
Identifiers
  • 7732-18-5
ECHA InfoCard 100.028.902
  • 962
  • DTXSID6026296
Properties
H2O
Molar mass 18.015 g·mol−1
Appearance Nearly colourless liquid or nearly colourless solid (blue if we look through thick layers of water) or colourless gas
Density Liquid:
0.9998396 g/mL at 0 °C
0.999972 at ~4 °C (Max.)
0.9970474 g/mL at 25 °C
Solid:
0.9167 g/mL at 0 °C
Melting point 0.00 °C (32.00 °F; 273.15 K)
Boiling point 99.98 °C (211.96 °F; 373.13 K)
Supplementary data page
Water (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
A globule of liquid water, and the concave depression and rebound in water caused by something dropping through the water surface
A block of solid water (ice)
Clouds in Earth's atmosphere condense from gaseous water vapor.

Because Earth's environment is relatively close to water's triple point, a number of natural states of water exist on earth.[3] It forms precipitation in the form of rain and aerosols in the form of fog. Clouds consist of suspended droplets of water and ice, its solid state. When finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is steam or water vapor.

Water covers about 71% of the Earth's surface, with seas and oceans making up most of the water volume on earth (about 96.5%).[4] Small portions of water occur as groundwater (1.7%), in the glaciers and the ice caps of Antarctica and Greenland (1.7%), and in the air as vapor, clouds (consisting of ice and liquid water suspended in air), and precipitation (0.001%).[5][6] Water moves continually through the water cycle of evaporation, transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea.

Water plays an important role in the world economy. Approximately 70% of the freshwater used by humans goes to agriculture.[7] Fishing in salt and fresh water bodies has been, and continues to be, a major source of food for many parts of the world, providing 6.5% of global protein.[8] Much of the long-distance trade of commodities (such as oil, natural gas, and manufactured products) is transported by boats through seas, rivers, lakes, and canals. Large quantities of water, ice, and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a wide variety of substances both mineral and organic; as such it is widely used in industrial processes, and in cooking and washing. Water, ice and snow are also central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, surfing, sport fishing, diving, ice skating and skiing.

Etymology

The word water comes from Old English wæter, from Proto-Germanic *watar (source also of Old Saxon watar, Old Frisian wetir, Dutch water, Old High German wazzar, German Wasser, vatn, Gothic 𐍅𐌰𐍄𐍉 (wato), from Proto-Indo-European *wod-or, suffixed form of root *wed- ("water"; "wet").[9] Also cognate, through the Indo-European root, with Greek ύδωρ (ýdor, from Ancient Greek ὕδωρ, hýdōr, whence English "hydro-"), Russian вода́ (vodá), Irish uisce, and Albanian ujë.

History

Main articles: Origin of water on Earth § History of water on Earth, and Properties of water § History

Properties

Main article: Properties of water
See also: Water (data page) and Water model
 
A water molecule consists of two hydrogen atoms and one oxygen atom

Water (H2O) is a polar inorganic compound. At room temperature it is a tasteless and odorless liquid, nearly colorless with a hint of blue. This simplest hydrogen chalcogenide is by far the most studied chemical compound and is described as the "universal solvent" for its ability to dissolve many substances.[10][11] This allows it to be the "solvent of life":[12] indeed, water as found in nature almost always includes various dissolved substances, and special steps are required to obtain chemically pure water. Water is the only common substance to exist as a solid, liquid, and gas in normal terrestrial conditions.[13]

States

 
The three common states of matter

Along with oxidane, water is one of the two official names for the chemical compound H
2O;[14] it is also the liquid phase of H
2O.[15] The other two common states of matter of water are the solid phase, ice, and the gaseous phase, water vapor or steam. The addition or removal of heat can cause phase transitions: freezing (water to ice), melting (ice to water), vaporization (water to vapor), condensation (vapor to water), sublimation (ice to vapor) and deposition (vapor to ice).[16]

Density

See also: Frost weathering

Water differs from most liquids in that it becomes less dense as it freezes.[a] In 1 atm pressure, it reaches its maximum density of 999.972 kg/m3 (62.4262 lb/cu ft) at 3.98 °C (39.16 °F), or almost 1,000 kg/m3 (62.43 lb/cu ft) at almost 4 °C (39 °F).[18][19] The density of ice is 917 kg/m3 (57.25 lb/cu ft), an expansion of 9%.[20][21] This expansion can exert enormous pressure, bursting pipes and cracking rocks.[22]

In a lake or ocean, water at 4 °C (39 °F) sinks to the bottom, and ice forms on the surface, floating on the liquid water. This ice insulates the water below, preventing it from freezing solid. Without this protection, most aquatic organisms residing in lakes would perish during the winter.[23]

Magnetism

Water is a diamagnetic material.[24] Though interaction is weak, with superconducting magnets it can attain a notable interaction.[24]

Phase transitions

At a pressure of one atmosphere (atm), ice melts or water freezes (solidifies) at 0 °C (32 °F)) and water boils or vapor condenses at 100 °C (212 °F). However, even below the boiling point, water can change to vapor at its surface by evaporation (vaporization throughout the liquid is known as boiling). Sublimation and deposition also occur on surfaces.[16] For example, frost is deposited on cold surfaces while snowflakes form by deposition on an aerosol particle or ice nucleus.[25] In the process of freeze-drying, a food is frozen and then stored at low pressure so the ice on its surface sublimates.[26]

The melting and boiling points depend on pressure. A good approximation for the rate of change of the melting temperature with pressure is given by the Clausius–Clapeyron relation:

 

where   and   are the molar volumes of the liquid and solid phases, and   is the molar latent heat of melting. In most substances, the volume increases when melting occurs, so the melting temperature increases with pressure. However, because ice is less dense than water, the melting temperature decreases.[17] In glaciers, pressure melting can occur under sufficiently thick volumes of ice, resulting in subglacial lakes.[27][28]

The Clausius-Clapeyron relation also applies to the boiling point, but with the liquid/gas transition the vapor phase has a much lower density than the liquid phase, so the boiling point increases with pressure.[29] Water can remain in a liquid state at high temperatures in the deep ocean or underground. For example, temperatures exceed 205 °C (401 °F) in Old Faithful, a geyser in Yellowstone National Park.[30] In hydrothermal vents, the temperature can exceed 400 °C (752 °F).[31]

At sea level, the boiling point of water is 100 °C (212 °F). As atmospheric pressure decreases with altitude, the boiling point decreases by 1 °C every 274 meters. High-altitude cooking takes longer than sea-level cooking. For example, at 1,524 metres (5,000 ft), cooking time must be increased by a fourth to achieve the desired result.[32] (Conversely, a pressure cooker can be used to decrease cooking times by raising the boiling temperature.[33]) In a vacuum, water will boil at room temperature.[34]

Triple and critical points

 
Phase diagram of water (simplified)

On a pressure/temperature phase diagram (see figure), there are curves separating solid from vapor, vapor from liquid, and liquid from solid. These meet at a single point called the triple point, where all three phases can coexist. The triple point is at a temperature of 273.16 K (0.01 °C; 32.02 °F) and a pressure of 611.657 pascals (0.00604 atm; 0.0887 psi);[35] it is the lowest pressure at which liquid water can exist. Until 2019, the triple point was used to define the Kelvin temperature scale.[36][37]

The water/vapor phase curve terminates at 647.096 K (373.946 °C; 705.103 °F) and 22.064 megapascals (3,200.1 psi; 217.75 atm).[38] This is known as the critical point. At higher temperatures and pressures the liquid and vapor phases form a continuous phase called a supercritical fluid. It can be gradually compressed or expanded between gas-like and liquid-like densities; its properties (which are quite different from those of ambient water) are sensitive to density. For example, for suitable pressures and temperatures it can mix freely with nonpolar compounds, including most organic compounds. This makes it useful in a variety of applications including high-temperature electrochemistry and as an ecologically benign solvent or catalyst in chemical reactions involving organic compounds. In Earth's mantle, it acts as a solvent during mineral formation, dissolution and deposition.[39][40]

Phases of ice and water

Main article: Ice

The normal form of ice on the surface of Earth is Ice Ih, a phase that forms crystals with hexagonal symmetry. Another with cubic crystalline symmetry, Ice Ic, can occur in the upper atmosphere.[41] As the pressure increases, ice forms other crystal structures. As of 2019, 17 have been experimentally confirmed and several more are predicted theoretically (see Ice).[42] The 18th form of ice, ice XVIII, a face-centred-cubic, superionic ice phase, was discovered when a droplet of water was subject to a shock wave that raised the water's pressure to millions of atmospheres and its temperature to thousands of degrees, resulting in a structure of rigid oxygen atoms in which hydrogen atoms flowed freely.[43][44] When sandwiched between layers of graphene, ice forms a square lattice.[45]

The details of the chemical nature of liquid water are not well understood; some theories suggest that its unusual behaviour is due to the existence of 2 liquid states.[19][46][47][48]

Taste and odor

Pure water is usually described as tasteless and odorless, although humans have specific sensors that can feel the presence of water in their mouths,[49][50] and frogs are known to be able to smell it.[51] However, water from ordinary sources (including bottled mineral water) usually has many dissolved substances, that may give it varying tastes and odors. Humans and other animals have developed senses that enable them to evaluate the potability of water in order to avoid water that is too salty or putrid.[52]

Color and appearance

Main article: Color of water
See also: Electromagnetic absorption by water

Pure water is visibly blue due to absorption of light in the region c. 600–800 nm.[53] The color can be easily observed in a glass of tap-water placed against a pure white background, in daylight. The principal absorption bands responsible for the color are overtones of the O–H stretching vibrations. The apparent intensity of the color increases with the depth of the water column, following Beer's law. This also applies, for example, with a swimming pool when the light source is sunlight reflected from the pool's white tiles.

In nature, the color may also be modified from blue to green due to the presence of suspended solids or algae.

In industry, near-infrared spectroscopy is used with aqueous solutions as the greater intensity of the lower overtones of water means that glass cuvettes with short path-length may be employed. To observe the fundamental stretching absorption spectrum of water or of an aqueous solution in the region around 3,500 cm−1 (2.85 μm)[54] a path length of about 25 μm is needed. Also, the cuvette must be both transparent around 3500 cm−1 and insoluble in water; calcium fluoride is one material that is in common use for the cuvette windows with aqueous solutions.

The Raman-active fundamental vibrations may be observed with, for example, a 1 cm sample cell.

Aquatic plants, algae, and other photosynthetic organisms can live in water up to hundreds of meters deep, because sunlight can reach them. Practically no sunlight reaches the parts of the oceans below 1,000 meters (3,300 ft) of depth.

The refractive index of liquid water (1.333 at 20 °C (68 °F)) is much higher than that of air (1.0), similar to those of alkanes and ethanol, but lower than those of glycerol (1.473), benzene (1.501), carbon disulfide (1.627), and common types of glass (1.4 to 1.6). The refraction index of ice (1.31) is lower than that of liquid water.

Polar molecule

 
Tetrahedral structure of water

In a water molecule, the hydrogen atoms form a 104.5° angle with the oxygen atom. The hydrogen atoms are close to two corners of a tetrahedron centered on the oxygen. At the other two corners are lone pairs of valence electrons that do not participate in the bonding. In a perfect tetrahedron, the atoms would form a 109.5° angle, but the repulsion between the lone pairs is greater than the repulsion between the hydrogen atoms.[55][56] The O–H bond length is about 0.096 nm.[57]

Other substances have a tetrahedral molecular structure, for example, methane (CH
4) and hydrogen sulfide (H
2S). However, oxygen is more electronegative (holds on to its electrons more tightly) than most other elements, so the oxygen atom retains a negative charge while the hydrogen atoms are positively charged. Along with the bent structure, this gives the molecule an electrical dipole moment and it is classified as a polar molecule.[58]

Water is a good polar solvent, that dissolves many salts and hydrophilic organic molecules such as sugars and simple alcohols such as ethanol. Water also dissolves many gases, such as oxygen and carbon dioxide—the latter giving the fizz of carbonated beverages, sparkling wines and beers. In addition, many substances in living organisms, such as proteins, DNA and polysaccharides, are dissolved in water. The interactions between water and the subunits of these biomacromolecules shape protein folding, DNA base pairing, and other phenomena crucial to life (hydrophobic effect).

Many organic substances (such as fats and oils and alkanes) are hydrophobic, that is, insoluble in water. Many inorganic substances are insoluble too, including most metal oxides, sulfides, and silicates.

Hydrogen bonding

See also: Chemical bonding of water
 
Model of hydrogen bonds (1) between molecules of water

Because of its polarity, a molecule of water in the liquid or solid state can form up to four hydrogen bonds with neighboring molecules. Hydrogen bonds are about ten times as strong as the Van der Waals force that attracts molecules to each other in most liquids. This is the reason why the melting and boiling points of water are much higher than those of other analogous compounds like hydrogen sulfide. They also explain its exceptionally high specific heat capacity (about 4.2 J/g/K), heat of fusion (about 333 J/g), heat of vaporization (2257 J/g), and thermal conductivity (between 0.561 and 0.679 W/m/K). These properties make water more effective at moderating Earth's climate, by storing heat and transporting it between the oceans and the atmosphere. The hydrogen bonds of water are around 23 kJ/mol (compared to a covalent O-H bond at 492 kJ/mol). Of this, it is estimated that 90% is attributable to electrostatics, while the remaining 10% is partially covalent.[59]

These bonds are the cause of water's high surface tension[60] and capillary forces. The capillary action refers to the tendency of water to move up a narrow tube against the force of gravity. This property is relied upon by all vascular plants, such as trees.[citation needed]

 
Specific heat capacity of water[61]

Self-ionization

Main article: Self-ionization of water

Water is a weak solution of hydronium hydroxide – there is an equilibrium 2H
2O ⇔ H
3O+
 + OH−
, in combination with solvation of the resulting hydronium ions.

Electrical conductivity and electrolysis

Pure water has a low electrical conductivity, which increases with the dissolution of a small amount of ionic material such as common salt.

Liquid water can be split into the elements hydrogen and oxygen by passing an electric current through it—a process called electrolysis. The decomposition requires more energy input than the heat released by the inverse process (285.8 kJ/mol, or 15.9 MJ/kg).[62]

Mechanical properties

Liquid water can be assumed to be incompressible for most purposes: its compressibility ranges from 4.4 to 5.1×10−10 Pa−1 in ordinary conditions.[63] Even in oceans at 4 km depth, where the pressure is 400 atm, water suffers only a 1.8% decrease in volume.[64]

The viscosity of water is about 10−3 Pa·s or 0.01 poise at 20 °C (68 °F), and the speed of sound in liquid water ranges between 1,400 and 1,540 meters per second (4,600 and 5,100 ft/s) depending on temperature. Sound travels long distances in water with little attenuation, especially at low frequencies (roughly 0.03 dB/km for 1 kHz), a property that is exploited by cetaceans and humans for communication and environment sensing (sonar).[65]

Reactivity

Metallic elements which are more electropositive than hydrogen, particularly the alkali metals and alkaline earth metals such as lithium, sodium, calcium, potassium and cesium displace hydrogen from water, forming hydroxides and releasing hydrogen. At high temperatures, carbon reacts with steam to form carbon monoxide and hydrogen.

On Earth

Main articles: Hydrology and Water distribution on Earth

Hydrology is the study of the movement, distribution, and quality of water throughout the Earth. The study of the distribution of water is hydrography. The study of the distribution and movement of groundwater is hydrogeology, of glaciers is glaciology, of inland waters is limnology and distribution of oceans is oceanography. Ecological processes with hydrology are in the focus of ecohydrology.

The collective mass of water found on, under, and over the surface of a planet is called the hydrosphere. Earth's approximate water volume (the total water supply of the world) is 1.386 billion cubic kilometres (333 million cubic miles).[5]

Liquid water is found in bodies of water, such as an ocean, sea, lake, river, stream, canal, pond, or puddle. The majority of water on Earth is seawater. Water is also present in the atmosphere in solid, liquid, and vapor states. It also exists as groundwater in aquifers.

Water is important in many geological processes. Groundwater is present in most rocks, and the pressure of this groundwater affects patterns of faulting. Water in the mantle is responsible for the melt that produces volcanoes at subduction zones. On the surface of the Earth, water is important in both chemical and physical weathering processes. Water, and to a lesser but still significant extent, ice, are also responsible for a large amount of sediment transport that occurs on the surface of the earth. Deposition of transported sediment forms many types of sedimentary rocks, which make up the geologic record of Earth history.

Water cycle

Main article: Water cycle

The water cycle (known scientifically as the hydrologic cycle) is the continuous exchange of water within the hydrosphere, between the atmosphere, soil water, surface water, groundwater, and plants.

Water moves perpetually through each of these regions in the water cycle consisting of the following transfer processes:

  • evaporation from oceans and other water bodies into the air and transpiration from land plants and animals into the air.
  • precipitation, from water vapor condensing from the air and falling to the earth or ocean.
  • runoff from the land usually reaching the sea.

Most water vapors found mostly in the ocean returns to it, but winds carry water vapor over land at the same rate as runoff into the sea, about 47 Tt per year whilst evaporation and transpiration happening in land masses also contribute another 72 Tt per year. Precipitation, at a rate of 119 Tt per year over land, has several forms: most commonly rain, snow, and hail, with some contribution from fog and dew.[66] Dew is small drops of water that are condensed when a high density of water vapor meets a cool surface. Dew usually forms in the morning when the temperature is the lowest, just before sunrise and when the temperature of the earth's surface starts to increase.[67] Condensed water in the air may also refract sunlight to produce rainbows.

Water runoff often collects over watersheds flowing into rivers. Through erosion, runoff shapes the environment creating river valleys and deltas which provide rich soil and level ground for the establishment of population centers. A flood occurs when an area of land, usually low-lying, is covered with water which occurs when a river overflows its banks or a storm surge happens. On the other hand, drought is an extended period of months or years when a region notes a deficiency in its water supply. This occurs when a region receives consistently below average precipitation either due to its topography or due to its location in terms of latitude.

Water resources

Main article: Water resources

Water resources are natural resources of water that are potentially useful for humans,[68] for example as a source of drinking water supply or irrigation water. Water occurs as both "stocks" and "flows". Water can be stored as lakes, water vapor, groundwater or aquifers, and ice and snow. Of the total volume of global freshwater, an estimated 69 percent is stored in glaciers and permanent snow cover; 30 percent is in groundwater; and the remaining 1 percent in lakes, rivers, the atmosphere, and biota.[69] The length of time water remains in storage is highly variable: some aquifers consist of water stored over thousands of years but lake volumes may fluctuate on a seasonal basis, decreasing during dry periods and increasing during wet ones. A substantial fraction of the water supply for some regions consists of water extracted from water stored in stocks, and when withdrawals exceed recharge, stocks decrease. By some estimates, as much as 30 percent of total water used for irrigation comes from unsustainable withdrawals of groundwater, causing groundwater depletion.[70]

Seawater and tides

Main articles: Seawater and Tides

Seawater contains about 3.5% sodium chloride on average, plus smaller amounts of other substances. The physical properties of seawater differ from fresh water in some important respects. It freezes at a lower temperature (about −1.9 °C (28.6 °F)) and its density increases with decreasing temperature to the freezing point, instead of reaching maximum density at a temperature above freezing. The salinity of water in major seas varies from about 0.7% in the Baltic Sea to 4.0% in the Red Sea. (The Dead Sea, known for its ultra-high salinity levels of between 30 and 40%, is really a salt lake.)

Tides are the cyclic rising and falling of local sea levels caused by the tidal forces of the Moon and the Sun acting on the oceans. Tides cause changes in the depth of the marine and estuarine water bodies and produce oscillating currents known as tidal streams. The changing tide produced at a given location is the result of the changing positions of the Moon and Sun relative to the Earth coupled with the effects of Earth rotation and the local bathymetry. The strip of seashore that is submerged at high tide and exposed at low tide, the intertidal zone, is an important ecological product of ocean tides.

The Bay of Fundy at high tide and low tide
  •  

    High tide

  •  

    Low tide

Effects on life

 
Overview of photosynthesis (green) and respiration (red)

From a biological standpoint, water has many distinct properties that are critical for the proliferation of life. It carries out this role by allowing organic compounds to react in ways that ultimately allow replication. All known forms of life depend on water. Water is vital both as a solvent in which many of the body's solutes dissolve and as an essential part of many metabolic processes within the body. Metabolism is the sum total of anabolism and catabolism. In anabolism, water is removed from molecules (through energy requiring enzymatic chemical reactions) in order to grow larger molecules (e.g., starches, triglycerides, and proteins for storage of fuels and information). In catabolism, water is used to break bonds in order to generate smaller molecules (e.g., glucose, fatty acids, and amino acids to be used for fuels for energy use or other purposes). Without water, these particular metabolic processes could not exist.

Water is fundamental to photosynthesis and respiration. Photosynthetic cells use the sun's energy to split off water's hydrogen from oxygen.[71] Hydrogen is combined with CO
2 (absorbed from air or water) to form glucose and release oxygen.[citation needed] All living cells use such fuels and oxidize the hydrogen and carbon to capture the sun's energy and reform water and CO
2 in the process (cellular respiration).

Water is also central to acid-base neutrality and enzyme function. An acid, a hydrogen ion (H+
, that is, a proton) donor, can be neutralized by a base, a proton acceptor such as a hydroxide ion (OH−
) to form water. Water is considered to be neutral, with a pH (the negative log of the hydrogen ion concentration) of 7. Acids have pH values less than 7 while bases have values greater than 7.

Aquatic life forms

Further information: Hydrobiology, Marine life, and Aquatic plant

Earth surface waters are filled with life. The earliest life forms appeared in water; nearly all fish live exclusively in water, and there are many types of marine mammals, such as dolphins and whales. Some kinds of animals, such as amphibians, spend portions of their lives in water and portions on land. Plants such as kelp and algae grow in the water and are the basis for some underwater ecosystems. Plankton is generally the foundation of the ocean food chain.

Aquatic vertebrates must obtain oxygen to survive, and they do so in various ways. Fish have gills instead of lungs, although some species of fish, such as the lungfish, have both. Marine mammals, such as dolphins, whales, otters, and seals need to surface periodically to breathe air. Some amphibians are able to absorb oxygen through their skin. Invertebrates exhibit a wide range of modifications to survive in poorly oxygenated waters including breathing tubes (see insect and mollusc siphons) and gills (Carcinus). However, as invertebrate life evolved in an aquatic habitat most have little or no specialization for respiration in water.

Effects on human civilization

 
Water fountain

Civilization has historically flourished around rivers and major waterways; Mesopotamia, one of the so-called cradles of civilization, was situated between the major rivers Tigris and Euphrates; the ancient society of the Egyptians depended entirely upon the Nile. The early Indus Valley civilization (c. 3300 BCE to 1300 BCE) developed along the Indus River and tributaries that flowed out of the Himalayas. Rome was also founded on the banks of the Italian river Tiber. Large metropolises like Rotterdam, London, Montreal, Paris, New York City, Buenos Aires, Shanghai, Tokyo, Chicago, and Hong Kong owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like Singapore, have flourished for the same reason. In places such as North Africa and the Middle East, where water is more scarce, access to clean drinking water was and is a major factor in human development.

Health and pollution

 
An environmental science program – a student from Iowa State University sampling water

Water fit for human consumption is called drinking water or potable water. Water that is not potable may be made potable by filtration or distillation, or by a range of other methods. More than 660 million people do not have access to safe drinking water.[72][73]

Water that is not fit for drinking but is not harmful to humans when used for swimming or bathing is called by various names other than potable or drinking water, and is sometimes called safe water, or "safe for bathing". Chlorine is a skin and mucous membrane irritant that is used to make water safe for bathing or drinking. Its use is highly technical and is usually monitored by government regulations (typically 1 part per million (ppm) for drinking water, and 1–2 ppm of chlorine not yet reacted with impurities for bathing water). Water for bathing may be maintained in satisfactory microbiological condition using chemical disinfectants such as chlorine or ozone or by the use of ultraviolet light.

Water reclamation is the process of converting wastewater (most commonly sewage, also called municipal wastewater) into water that can be reused for other purposes. There are 2.3 billion people who reside in nations with water scarcities, which means that each individual receives less than 1,700 cubic metres (60,000 cu ft) of water annually. 380 billion cubic metres (13×10^12 cu ft) of municipal wastewater are produced globally each year.[74][75][76]

Freshwater is a renewable resource, recirculated by the natural hydrologic cycle, but pressures over access to it result from the naturally uneven distribution in space and time, growing economic demands by agriculture and industry, and rising populations. Currently, nearly a billion people around the world lack access to safe, affordable water. In 2000, the United Nations established the Millennium Development Goals for water to halve by 2015 the proportion of people worldwide without access to safe water and sanitation. Progress toward that goal was uneven, and in 2015 the UN committed to the Sustainable Development Goals of achieving universal access to safe and affordable water and sanitation by 2030. Poor water quality and bad sanitation are deadly; some five million deaths a year are caused by water-related diseases. The World Health Organization estimates that safe water could prevent 1.4 million child deaths from diarrhoea each year.[77]

In developing countries, 90% of all municipal wastewater still goes untreated into local rivers and streams.[78] Some 50 countries, with roughly a third of the world's population, also suffer from medium or high water scarcity and 17 of these extract more water annually than is recharged through their natural water cycles.[79] The strain not only affects surface freshwater bodies like rivers and lakes, but it also degrades groundwater resources.

Human uses

Further information: Water supply
 
Total water withdrawals for agricultural, industrial and municipal purposes per capita, measured in cubic metres (m3) per year in 2010[80]

Agriculture

The most substantial human use of water is for agriculture, including irrigated agriculture, which accounts for as much as 80 to 90 percent of total human water consumption.[81] In the United States, 42% of freshwater withdrawn for use is for irrigation, but the vast majority of water "consumed" (used and not returned to the environment) goes to agriculture.[82]

Access to fresh water is often taken for granted, especially in developed countries that have built sophisticated water systems for collecting, purifying, and delivering water, and removing wastewater. But growing economic, demographic, and climatic pressures are increasing concerns about water issues, leading to increasing competition for fixed water resources, giving rise to the concept of peak water.[83] As populations and economies continue to grow, consumption of water-thirsty meat expands, and new demands rise for biofuels or new water-intensive industries, new water challenges are likely.[84]

An assessment of water management in agriculture was conducted in 2007 by the International Water Management Institute in Sri Lanka to see if the world had sufficient water to provide food for its growing population.[85] It assessed the current availability of water for agriculture on a global scale and mapped out locations suffering from water scarcity. It found that a fifth of the world's people, more than 1.2 billion, live in areas of physical water scarcity, where there is not enough water to meet all demands. A further 1.6 billion people live in areas experiencing economic water scarcity, where the lack of investment in water or insufficient human capacity make it impossible for authorities to satisfy the demand for water. The report found that it would be possible to produce the food required in the future, but that continuation of today's food production and environmental trends would lead to crises in many parts of the world. To avoid a global water crisis, farmers will have to strive to increase productivity to meet growing demands for food, while industries and cities find ways to use water more efficiently.[86]

Water scarcity is also caused by production of water intensive products. For example, cotton: 1 kg of cotton—equivalent of a pair of jeans—requires 10.9 cubic meters (380 cu ft) water to produce. While cotton accounts for 2.4% of world water use, the water is consumed in regions that are already at a risk of water shortage. Significant environmental damage has been caused: for example, the diversion of water by the former Soviet Union from the Amu Darya and Syr Darya rivers to produce cotton was largely responsible for the disappearance of the Aral Sea.[87]

  •  

    Water requirement per tonne of food product

  • Water distribution in subsurface drip irrigation

  •  

    Irrigation of field crops

As a scientific standard

On 7 April 1795, the gram was defined in France to be equal to "the absolute weight of a volume of pure water equal to a cube of one-hundredth of a meter, and at the temperature of melting ice".[88] For practical purposes though, a metallic reference standard was required, one thousand times more massive, the kilogram. Work was therefore commissioned to determine precisely the mass of one liter of water. In spite of the fact that the decreed definition of the gram specified water at 0 °C (32 °F)—a highly reproducible temperature—the scientists chose to redefine the standard and to perform their measurements at the temperature of highest water density, which was measured at the time as 4 °C (39 °F).[89]

The Kelvin temperature scale of the SI system was based on the triple point of water, defined as exactly 273.16 K (0.01 °C; 32.02 °F), but as of May 2019 is based on the Boltzmann constant instead. The scale is an absolute temperature scale with the same increment as the Celsius temperature scale, which was originally defined according to the boiling point (set to 100 °C (212 °F)) and melting point (set to 0 °C (32 °F)) of water.

Natural water consists mainly of the isotopes hydrogen-1 and oxygen-16, but there is also a small quantity of heavier isotopes oxygen-18, oxygen-17, and hydrogen-2 (deuterium). The percentage of the heavier isotopes is very small, but it still affects the properties of water. Water from rivers and lakes tends to contain less heavy isotopes than seawater. Therefore, standard water is defined in the Vienna Standard Mean Ocean Water specification.

For drinking

Main article: Drinking water
 
A young girl drinking bottled water
 
Water availability: the fraction of the population using improved water sources by country
 
Roadside fresh water outlet from glacier, Nubra

The human body contains from 55% to 78% water, depending on body size.[90][user-generated source?] To function properly, the body requires between one and seven liters (0.22 and 1.54 imp gal; 0.26 and 1.85 U.S. gal)[citation needed] of water per day to avoid dehydration; the precise amount depends on the level of activity, temperature, humidity, and other factors. Most of this is ingested through foods or beverages other than drinking straight water. It is not clear how much water intake is needed by healthy people, though the British Dietetic Association advises that 2.5 liters of total water daily is the minimum to maintain proper hydration, including 1.8 liters (6 to 7 glasses) obtained directly from beverages.[91] Medical literature favors a lower consumption, typically 1 liter of water for an average male, excluding extra requirements due to fluid loss from exercise or warm weather.[92]

Healthy kidneys can excrete 0.8 to 1 liter of water per hour, but stress such as exercise can reduce this amount. People can drink far more water than necessary while exercising, putting them at risk of water intoxication (hyperhydration), which can be fatal.[93][94] The popular claim that "a person should consume eight glasses of water per day" seems to have no real basis in science.[95] Studies have shown that extra water intake, especially up to 500 milliliters (18 imp fl oz; 17 U.S. fl oz) at mealtime, was associated with weight loss.[96][97][98][99][100][101] Adequate fluid intake is helpful in preventing constipation.[102]

 
Hazard symbol for non-potable water

An original recommendation for water intake in 1945 by the Food and Nutrition Board of the U.S. National Research Council read: "An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods."[103] The latest dietary reference intake report by the U.S. National Research Council in general recommended, based on the median total water intake from US survey data (including food sources): 3.7 liters (0.81 imp gal; 0.98 U.S. gal) for men and 2.7 liters (0.59 imp gal; 0.71 U.S. gal) of water total for women, noting that water contained in food provided approximately 19% of total water intake in the survey.[104]

Specifically, pregnant and breastfeeding women need additional fluids to stay hydrated. The US Institute of Medicine recommends that, on average, men consume 3 liters (0.66 imp gal; 0.79 U.S. gal) and women 2.2 liters (0.48 imp gal; 0.58 U.S. gal); pregnant women should increase intake to 2.4 liters (0.53 imp gal; 0.63 U.S. gal) and breastfeeding women should get 3 liters (12 cups), since an especially large amount of fluid is lost during nursing.[105] Also noted is that normally, about 20% of water intake comes from food, while the rest comes from drinking water and beverages (caffeinated included). Water is excreted from the body in multiple forms; through urine and feces, through sweating, and by exhalation of water vapor in the breath. With physical exertion and heat exposure, water loss will increase and daily fluid needs may increase as well.

Humans require water with few impurities. Common impurities include metal salts and oxides, including copper, iron, calcium and lead,[106][full citation needed] and/or harmful bacteria, such as Vibrio. Some solutes are acceptable and even desirable for taste enhancement and to provide needed electrolytes.[107]

The single largest (by volume) freshwater resource suitable for drinking is Lake Baikal in Siberia.[108]

Washing

This section is an excerpt from Washing.[edit]
 
A woman washes her hands with soap and water.

Washing is a method of cleaning, usually with water and soap or detergent. Washing and then rinsing both body and clothing is an essential part of good hygiene and health. [citation needed]

Often people use soaps and detergents to assist in the emulsification of oils and dirt particles so they can be washed away. The soap can be applied directly, or with the aid of a washcloth.

People wash themselves, or bathe periodically for religious ritual or therapeutic purposes[109] or as a recreational activity.

In Europe, some people use a bidet to wash their external genitalia and the anal region after using the toilet, instead of using toilet paper.[110] The bidet is common in predominantly Catholic countries where water is considered essential for anal cleansing.[111]

More frequent is washing of just the hands, e.g. before and after preparing food and eating, after using the toilet, after handling something dirty, etc. Hand washing is important in reducing the spread of germs.[112][113][114] Also common is washing the face, which is done after waking up, or to keep oneself cool during the day. Brushing one's teeth is also essential for hygiene and is a part of washing.

'Washing' can also refer to the washing of clothing or other cloth items, like bedsheets, whether by hand or with a washing machine. It can also refer to washing one's car, by lathering the exterior with car soap, then rinsing it off with a hose, or washing cookware.

 
A private home washing machine
Excessive washing may damage the hair, causing dandruff, or cause rough skin/skin lesions.[115][116]

Transportation

These paragraphs are an excerpt from Maritime transport.[edit]

Maritime transport (or ocean transport) or more generally waterborne transport, is the transport of people (passengers) or goods (cargo) via waterways. Freight transport by sea has been widely used throughout recorded history. The advent of aviation has diminished the importance of sea travel for passengers, though it is still popular for short trips and pleasure cruises. Transport by water is cheaper than transport by air,[117] despite fluctuating exchange rates and a fee placed on top of freighting charges for carrier companies known as the currency adjustment factor. Maritime transport accounts for roughly 80% of international trade, according to UNCTAD in 2020.

Maritime transport can be realized over any distance by boat, ship, sailboat or barge, over oceans and lakes, through canals or along rivers. Shipping may be for commerce, recreation, or military purposes. While extensive inland shipping is less critical today, the major waterways of the world including many canals are still very important and are integral parts of worldwide economies. Particularly, especially any material can be moved by water; however, water transport becomes impractical when material delivery is time-critical such as various types of perishable produce. Still, water transport is highly cost effective with regular schedulable cargoes, such as trans-oceanic shipping of consumer products – and especially for heavy loads or bulk cargos, such as coal, coke, ores, or grains. Arguably, the industrial revolution took place best where cheap water transport by canal, navigations, or shipping by all types of watercraft on natural waterways supported cost-effective bulk transport.

Containerization revolutionized maritime transport starting in the 1970s. "General cargo" includes goods packaged in boxes, cases, pallets, and barrels. When a cargo is carried in more than one mode, it is intermodal or co-modal.

Chemical uses

Water is widely used in chemical reactions as a solvent or reactant and less commonly as a solute or catalyst. In inorganic reactions, water is a common solvent, dissolving many ionic compounds, as well as other polar compounds such as ammonia and compounds closely related to water. In organic reactions, it is not usually used as a reaction solvent, because it does not dissolve the reactants well and is amphoteric (acidic and basic) and nucleophilic. Nevertheless, these properties are sometimes desirable. Also, acceleration of Diels-Alder reactions by water has been observed. Supercritical water has recently been a topic of research. Oxygen-saturated supercritical water combusts organic pollutants efficiently.

Heat exchange

Water and steam are a common fluid used for heat exchange, due to its availability and high heat capacity, both for cooling and heating. Cool water may even be naturally available from a lake or the sea. It is especially effective to transport heat through vaporization and condensation of water because of its large latent heat of vaporization. A disadvantage is that metals commonly found in industries such as steel and copper are oxidized faster by untreated water and steam. In almost all thermal power stations, water is used as the working fluid (used in a closed-loop between boiler, steam turbine, and condenser), and the coolant (used to exchange the waste heat to a water body or carry it away by evaporation in a cooling tower). In the United States, cooling power plants is the largest use of water.[118]

In the nuclear power industry, water can also be used as a neutron moderator. In most nuclear reactors, water is both a coolant and a moderator. This provides something of a passive safety measure, as removing the water from the reactor also slows the nuclear reaction down. However other methods are favored for stopping a reaction and it is preferred to keep the nuclear core covered with water so as to ensure adequate cooling.

Fire considerations

 
Water is used for fighting wildfires.

Water has a high heat of vaporization and is relatively inert, which makes it a good fire extinguishing fluid. The evaporation of water carries heat away from the fire. It is dangerous to use water on fires involving oils and organic solvents because many organic materials float on water and the water tends to spread the burning liquid.

Use of water in fire fighting should also take into account the hazards of a steam explosion, which may occur when water is used on very hot fires in confined spaces, and of a hydrogen explosion, when substances which react with water, such as certain metals or hot carbon such as coal, charcoal, or coke graphite, decompose the water, producing water gas.

The power of such explosions was seen in the Chernobyl disaster, although the water involved in this case did not come from fire-fighting but from the reactor's own water cooling system. A steam explosion occurred when the extreme overheating of the core caused water to flash into steam. A hydrogen explosion may have occurred as a result of a reaction between steam and hot zirconium.

Some metallic oxides, most notably those of alkali metals and alkaline earth metals, produce so much heat on reaction with water that a fire hazard can develop. The alkaline earth oxide quicklime is a mass-produced substance that is often transported in paper bags. If these are soaked through, they may ignite as their contents react with water.[119]

Recreation

Main article: Water sport (recreation)

Humans use water for many recreational purposes, as well as for exercising and for sports. Some of these include swimming, waterskiing, boating, surfing and diving. In addition, some sports, like ice hockey and ice skating, are played on ice. Lakesides, beaches and water parks are popular places for people to go to relax and enjoy recreation. Many find the sound and appearance of flowing water to be calming, and fountains and other flowing water structures are popular decorations. Some keep fish and other flora and fauna inside aquariums or ponds for show, fun, and companionship. Humans also use water for snow sports such as skiing, sledding, snowmobiling or snowboarding, which the require the water to be at a low temperature either as ice or crystallized into snow.

Water industry

The water industry provides drinking water and wastewater services (including sewage treatment) to households and industry. Water supply facilities include water wells, cisterns for rainwater harvesting, water supply networks, and water purification facilities, water tanks, water towers, water pipes including old aqueducts. Atmospheric water generators are in development.

Drinking water is often collected at springs, extracted from artificial borings (wells) in the ground, or pumped from lakes and rivers. Building more wells in adequate places is thus a possible way to produce more water, assuming the aquifers can supply an adequate flow. Other water sources include rainwater collection. Water may require purification for human consumption. This may involve the removal of undissolved substances, dissolved substances and harmful microbes. Popular methods are filtering with sand which only removes undissolved material, while chlorination and boiling kill harmful microbes. Distillation does all three functions. More advanced techniques exist, such as reverse osmosis. Desalination of abundant seawater is a more expensive solution used in coastal arid climates.

The distribution of drinking water is done through municipal water systems, tanker delivery or as bottled water. Governments in many countries have programs to distribute water to the needy at no charge.

Reducing usage by using drinking (potable) water only for human consumption is another option. In some cities such as Hong Kong, seawater is extensively used for flushing toilets citywide in order to conserve freshwater resources.

Polluting water may be the biggest single misuse of water; to the extent that a pollutant limits other uses of the water, it becomes a waste of the resource, regardless of benefits to the polluter. Like other types of pollution, this does not enter standard accounting of market costs, being conceived as externalities for which the market cannot account. Thus other people pay the price of water pollution, while the private firms' profits are not redistributed to the local population, victims of this pollution. Pharmaceuticals consumed by humans often end up in the waterways and can have detrimental effects on aquatic life if they bioaccumulate and if they are not biodegradable.

Municipal and industrial wastewater are typically treated at wastewater treatment plants. Mitigation of polluted surface runoff is addressed through a variety of prevention and treatment techniques. (See Surface runoff#Mitigation and treatment.)

Industrial applications

Many industrial processes rely on reactions using chemicals dissolved in water, suspension of solids in water slurries or using water to dissolve and extract substances, or to wash products or process equipment. Processes such as mining, chemical pulping, pulp bleaching, paper manufacturing, textile production, dyeing, printing, and cooling of power plants use large amounts of water, requiring a dedicated water source, and often cause significant water pollution.

Water is used in power generation. Hydroelectricity is electricity obtained from hydropower. Hydroelectric power comes from water driving a water turbine connected to a generator. Hydroelectricity is a low-cost, non-polluting, renewable energy source. The energy is supplied by the motion of water. Typically a dam is constructed on a river, creating an artificial lake behind it. Water flowing out of the lake is forced through turbines that turn generators.

 
Three Gorges Dam is the largest hydro-electric power station in the world.

Pressurized water is used in water blasting and water jet cutters. Also, high pressure water guns are used for precise cutting. It works very well, is relatively safe, and is not harmful to the environment. It is also used in the cooling of machinery to prevent overheating, or prevent saw blades from overheating.

Water is also used in many industrial processes and machines, such as the steam turbine and heat exchanger, in addition to its use as a chemical solvent. Discharge of untreated water from industrial uses is pollution. Pollution includes discharged solutes (chemical pollution) and discharged coolant water (thermal pollution). Industry requires pure water for many applications and uses a variety of purification techniques both in water supply and discharge.

Food processing

 
Water can be used to cook foods such as noodles
 
Sterile water for injection

Boiling, steaming, and simmering are popular cooking methods that often require immersing food in water or its gaseous state, steam.[120] Water is also used for dishwashing. Water also plays many critical roles within the field of food science.

Solutes such as salts and sugars found in water affect the physical properties of water. The boiling and freezing points of water are affected by solutes, as well as air pressure, which is in turn affected by altitude. Water boils at lower temperatures with the lower air pressure that occurs at higher elevations. One mole of sucrose (sugar) per kilogram of water raises the boiling point of water by 0.51 °C (0.918 °F), and one mole of salt per kg raises the boiling point by 1.02 °C (1.836 °F); similarly, increasing the number of dissolved particles lowers water's freezing point.[121]

Solutes in water also affect water activity that affects many chemical reactions and the growth of microbes in food.[122] Water activity can be described as a ratio of the vapor pressure of water in a solution to the vapor pressure of pure water.[121] Solutes in water lower water activity—this is important to know because most bacterial growth ceases at low levels of water activity.[122] Not only does microbial growth affect the safety of food, but also the preservation and shelf life of food.

Water hardness is also a critical factor in food processing and may be altered or treated by using a chemical ion exchange system. It can dramatically affect the quality of a product, as well as playing a role in sanitation. Water hardness is classified based on concentration of calcium carbonate the water contains. Water is classified as soft if it contains less than 100 mg/L (UK)[123] or less than 60 mg/L (US).[124]

According to a report published by the Water Footprint organization in 2010, a single kilogram of beef requires 15 thousand liters (3.3×10^3 imp gal; 4.0×10^3 U.S. gal) of water; however, the authors also make clear that this is a global average and circumstantial factors determine the amount of water used in beef production.[125]

Medical use

Water for injection is on the World Health Organization's list of essential medicines.[126]

Distribution in nature

In the universe

 
Band 5 ALMA receiver is an instrument specifically designed to detect water in the universe.[127]

Much of the universe's water is produced as a byproduct of star formation. The formation of stars is accompanied by a strong outward wind of gas and dust. When this outflow of material eventually impacts the surrounding gas, the shock waves that are created compress and heat the gas. The water observed is quickly produced in this warm dense gas.[128]

On 22 July 2011, a report described the discovery of a gigantic cloud of water vapor containing "140 trillion times more water than all of Earth's oceans combined" around a quasar located 12 billion light years from Earth. According to the researchers, the "discovery shows that water has been prevalent in the universe for nearly its entire existence".[129][130]

Water has been detected in interstellar clouds within the Milky Way.[131] Water probably exists in abundance in other galaxies, too, because its components, hydrogen, and oxygen, are among the most abundant elements in the universe. Based on models of the formation and evolution of the Solar System and that of other star systems, most other planetary systems are likely to have similar ingredients.

Water vapor

Water is present as vapor in:

Liquid water

Liquid water is present on Earth, covering 71% of its surface.[4] Liquid water is also occasionally present in small amounts on Mars.[152] Scientists believe liquid water is present in the Saturnian moons of Enceladus, as a 10-kilometre thick ocean approximately 30–40 kilometres below Enceladus' south polar surface,[153][154] and Titan, as a subsurface layer, possibly mixed with ammonia.[155] Jupiter's moon Europa has surface characteristics which suggest a subsurface liquid water ocean.[156] Liquid water may also exist on Jupiter's moon Ganymede as a layer sandwiched between high pressure ice and rock.[157]

Water ice

Water is present as ice on:

 
South polar ice cap of Mars during Martian south summer 2000

And is also likely present on:

Exotic forms

Water and other volatiles probably comprise much of the internal structures of Uranus and Neptune and the water in the deeper layers may be in the form of ionic water in which the molecules break down into a soup of hydrogen and oxygen ions, and deeper still as superionic water in which the oxygen crystallizes, but the hydrogen ions float about freely within the oxygen lattice.[176]

Water and planetary habitability

Further information: Water distribution on Earth and Planetary habitability

The existence of liquid water, and to a lesser extent its gaseous and solid forms, on Earth are vital to the existence of life on Earth as we know it. The Earth is located in the habitable zone of the Solar System; if it were slightly closer to or farther from the Sun (about 5%, or about 8 million kilometers), the conditions which allow the three forms to be present simultaneously would be far less likely to exist.[177][178]

Earth's gravity allows it to hold an atmosphere. Water vapor and carbon dioxide in the atmosphere provide a temperature buffer (greenhouse effect) which helps maintain a relatively steady surface temperature. If Earth were smaller, a thinner atmosphere would allow temperature extremes, thus preventing the accumulation of water except in polar ice caps (as on Mars).[citation needed]

The surface temperature of Earth has been relatively constant through geologic time despite varying levels of incoming solar radiation (insolation), indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the Gaia hypothesis.[citation needed]

The state of water on a planet depends on ambient pressure, which is determined by the planet's gravity. If a planet is sufficiently massive, the water on it may be solid even at high temperatures, because of the high pressure caused by gravity, as it was observed on exoplanets Gliese 436 b[179] and GJ 1214 b.[180]

Law, politics, and crisis

Main articles: Water law, Water right, and Water crisis
 
An estimate of the proportion of people in developing countries with access to potable water 1970–2000

Water politics is politics affected by water and water resources. Water, particularly fresh water, is a strategic resource across the world and an important element in many political conflicts. It causes health impacts and damage to biodiversity.

Access to safe drinking water has improved over the last decades in almost every part of the world, but approximately one billion people still lack access to safe water and over 2.5 billion lack access to adequate sanitation.[181] However, some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability.[182] A report, issued in November 2009, suggests that by 2030, in some developing regions of the world, water demand will exceed supply by 50%.[183]

1.6 billion people have gained access to a safe water source since 1990.[184] The proportion of people in developing countries with access to safe water is calculated to have improved from 30% in 1970[185] to 71% in 1990, 79% in 2000, and 84% in 2004.[181]

A 2006 United Nations report stated that "there is enough water for everyone", but that access to it is hampered by mismanagement and corruption.[186] In addition, global initiatives to improve the efficiency of aid delivery, such as the Paris Declaration on Aid Effectiveness, have not been taken up by water sector donors as effectively as they have in education and health, potentially leaving multiple donors working on overlapping projects and recipient governments without empowerment to act.[187]

The authors of the 2007 Comprehensive Assessment of Water Management in Agriculture cited poor governance as one reason for some forms of water scarcity. Water governance is the set of formal and informal processes through which decisions related to water management are made. Good water governance is primarily about knowing what processes work best in a particular physical and socioeconomic context. Mistakes have sometimes been made by trying to apply 'blueprints' that work in the developed world to developing world locations and contexts. The Mekong river is one example; a review by the International Water Management Institute of policies in six countries that rely on the Mekong river for water found that thorough and transparent cost-benefit analyses and environmental impact assessments were rarely undertaken. They also discovered that Cambodia's draft water law was much more complex than it needed to be.[188]

The UN World Water Development Report (WWDR, 2003) from the World Water Assessment Program indicates that, in the next 20 years, the quantity of water available to everyone is predicted to decrease by 30%. 40% of the world's inhabitants currently have insufficient fresh water for minimal hygiene. More than 2.2 million people died in 2000 from waterborne diseases (related to the consumption of contaminated water) or drought. In 2004, the UK charity WaterAid reported that a child dies every 15 seconds from easily preventable water-related diseases; often this means lack of sewage disposal.[citation needed]

Organizations concerned with water protection include the International Water Association (IWA), WaterAid, Water 1st, and the American Water Resources Association. The International Water Management Institute undertakes projects with the aim of using effective water management to reduce poverty. Water related conventions are United Nations Convention to Combat Desertification (UNCCD), International Convention for the Prevention of Pollution from Ships, United Nations Convention on the Law of the Sea and Ramsar Convention. World Day for Water takes place on 22 March[189] and World Oceans Day on 8 June.[190]

In culture

Religion

Main article: Water and religion
See also: Sacred waters
 
People come to Inda Abba Hadera spring (Inda Sillasie, Ethiopia) to wash in holy water

Water is considered a purifier in most religions. Faiths that incorporate ritual washing (ablution) include Christianity,[191] Hinduism, Islam, Judaism, the Rastafari movement, Shinto, Taoism, and Wicca. Immersion (or aspersion or affusion) of a person in water is a central Sacrament of Christianity (where it is called baptism); it is also a part of the practice of other religions, including Islam (Ghusl), Judaism (mikvah) and Sikhism (Amrit Sanskar). In addition, a ritual bath in pure water is performed for the dead in many religions including Islam and Judaism. In Islam, the five daily prayers can be done in most cases after washing certain parts of the body using clean water (wudu), unless water is unavailable (see Tayammum). In Shinto, water is used in almost all rituals to cleanse a person or an area (e.g., in the ritual of misogi).

In Christianity, holy water is water that has been sanctified by a priest for the purpose of baptism, the blessing of persons, places, and objects, or as a means of repelling evil.[192][193]

In Zoroastrianism, water (āb) is respected as the source of life.[194]

Philosophy

 
Icosahedron as a part of Spinoza monument in Amsterdam.

The Ancient Greek philosopher Empedocles saw water as one of the four classical elements (along with fire, earth, and air), and regarded it as an ylem, or basic substance of the universe. Thales, whom Aristotle portrayed as an astronomer and an engineer, theorized that the earth, which is denser than water, emerged from the water. Thales, a monist, believed further that all things are made from water. Plato believed that the shape of water is an icosahedron – flowing easily compared to the cube-shaped earth.[195]

The theory of the four bodily humors associated water with phlegm, as being cold and moist. The classical element of water was also one of the five elements in traditional Chinese philosophy (along with earth, fire, wood, and metal).

Some traditional and popular Asian philosophical systems take water as a role-model. James Legge's 1891 translation of the Dao De Jing states, "The highest excellence is like (that of) water. The excellence of water appears in its benefiting all things, and in its occupying, without striving (to the contrary), the low place which all men dislike. Hence (its way) is near to (that of) the Tao" and "There is nothing in the world more soft and weak than water, and yet for attacking things that are firm and strong there is nothing that can take precedence of it—for there is nothing (so effectual) for which it can be changed."[196] Guanzi in the "Shui di" 水地 chapter further elaborates on the symbolism of water, proclaiming that "man is water" and attributing natural qualities of the people of different Chinese regions to the character of local water resources.[197]

Folklore

"Living water" features in Germanic and Slavic folktales as a means of bringing the dead back to life. Note the Grimm fairy-tale ("The Water of Life") and the Russian dichotomy of living [ru] and dead water [ru]. The Fountain of Youth represents a related concept of magical waters allegedly preventing aging.

Art and activism

Painter and activist Fredericka Foster curated The Value of Water, at the Cathedral of St. John the Divine in New York City,[198] which anchored a year-long initiative by the Cathedral on our dependence on water.[199][200] The largest exhibition to ever appear at the Cathedral,[201] it featured over forty artists, including Jenny Holzer, Robert Longo, Mark Rothko, William Kentridge, April Gornik, Kiki Smith, Pat Steir, William Kentridge, Alice Dalton Brown, Teresita Fernandez and Bill Viola.[202][203] Foster created Think About Water,[204][full citation needed] an ecological collective of artists who use water as their subject or medium. Members include Basia Irland,[205][full citation needed] Aviva Rahmani, Betsy Damon, Diane Burko, Leila Daw, Stacy Levy, Charlotte Coté,[206] Meridel Rubenstein, Stacy Levy, Anna Macleod, and Aviva Rahmani.

To mark the 10th anniversary of access to water and sanitation being declared a human right by the UN, the charity WaterAid commissioned ten visual artists to show the impact of clean water on people's lives.[207][208]

Dihydrogen monoxide parody

Main article: Dihydrogen monoxide parody

Water's technically correct but rarely used chemical name, dihydrogen monoxide, has been used in a series of hoaxes and pranks that mock scientific illiteracy. This began in 1983, when an April Fools' Day article appeared in a newspaper in Durand, Michigan. The false story consisted of safety concerns about the substance.[209]

See also

Notes

  1. ^ Other substances with this property include bismuth, silicon, germanium and gallium.[17]

References

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Works cited

  • Ball, Philip (2001). Life's matrix : a biography of water (1st ed.). Farrar, Straus, and Giroux. ISBN 9780520230088.
  • Franks, Felix (2007). Water : a matrix of life (2nd ed.). Royal Society of Chemistry. ISBN 9781847552341.

Further reading

  • Debenedetti, PG., and HE Stanley, "Supercooled and Glassy Water", Physics Today 56 (6), pp. 40–46 (2003). Downloadable PDF (1.9 MB) 1 November 2018 at the Wayback Machine
  • Gleick, PH., (editor), The World's Water: The Biennial Report on Freshwater Resources. Island Press, Washington, D.C. (published every two years, beginning in 1998.) The World's Water, Island Press 26 February 2009 at the Wayback Machine
  • Jones, Oliver A.; Lester, John N.; Voulvoulis, Nick (2005). "Pharmaceuticals: a threat to drinking water?". Trends in Biotechnology. 23 (4): 163–167. doi:10.1016/j.tibtech.2005.02.001. PMID 15780706.
  • Journal of Contemporary Water Research & Education 3 March 2016 at the Wayback Machine
  • Postel, S., Last Oasis: Facing Water Scarcity. W.W. Norton and Company, New York. 1992
  • Reisner, M., Cadillac Desert: The American West and Its Disappearing Water. Penguin Books, New York. 1986.
  • United Nations World Water Development Report 22 February 2009 at the Wayback Machine. Produced every three years.
  • St. Fleur, Nicholas. The Water in Your Glass Might Be Older Than the Sun 15 January 2017 at the Wayback Machine. "The water you drink is older than the planet you're standing on." The New York Times (15 April 2016)

External links

  • OECD Water statistics
  • The World's Water Data Page
  • FAO Comprehensive Water Database, AQUASTAT
  • The Water Conflict Chronology: Water Conflict Database 16 January 2013 at the Wayback Machine
  • Water science school (USGS)
  • Portal to The World Bank's strategy, work and associated publications on water resources
  • America Water Resources Association 24 March 2018 at the Wayback Machine
  • Water on the web
  • Water structure and science 28 December 2014 at the Wayback Machine
  • "Why water is one of the weirdest things in the universe", Ideas, BBC, Video, 3:16 minutes, 2019
  • The chemistry of water 19 June 2020 at the Wayback Machine (NSF special report)
  • The International Association for the Properties of Water and Steam
  • H2O: The Molecule That Made Us, a 2020 PBS documentary

February 15, 2023
water, other, uses, disambiguation, redirect, here, other, uses, disambiguation, disambiguation, inorganic, compound, with, chemical, formula, transparent, tasteless, odorless, nearly, colorless, chemical, substance, which, main, constituent, earth, hydrospher. For other uses see Water disambiguation H2O and H20 redirect here For other uses see H20 disambiguation and H O disambiguation Water is an inorganic compound with the chemical formula H2O It is a transparent tasteless odorless and nearly colorless chemical substance which is the main constituent of Earth s hydrosphere and the fluids of all known living organisms in which it acts as a solvent 1 It is vital for all known forms of life despite not providing food energy or organic micronutrients Its chemical formula H2O indicates that each of its molecules contains one oxygen and two hydrogen atoms connected by covalent bonds The hydrogen atoms are attached to the oxygen atom at an angle of 104 45 2 Water is also the name of the liquid state of H2O at standard temperature and pressure Water NamesIUPAC name WaterSystematic IUPAC name OxidaneIdentifiersCAS Number 7732 18 5ECHA InfoCard 100 028 902PubChem CID 962CompTox Dashboard EPA DTXSID6026296PropertiesChemical formula H2OMolar mass 18 015 g mol 1Appearance Nearly colourless liquid or nearly colourless solid blue if we look through thick layers of water or colourless gasDensity Liquid 0 9998396 g mL at 0 C0 999972 at 4 C Max 0 9970474 g mL at 25 CSolid 0 9167 g mL at 0 CMelting point 0 00 C 32 00 F 273 15 K Boiling point 99 98 C 211 96 F 373 13 K Supplementary data pageWater data page Except where otherwise noted data are given for materials in their standard state at 25 C 77 F 100 kPa Infobox references A globule of liquid water and the concave depression and rebound in water caused by something dropping through the water surfaceA block of solid water ice Clouds in Earth s atmosphere condense from gaseous water vapor Because Earth s environment is relatively close to water s triple point a number of natural states of water exist on earth 3 It forms precipitation in the form of rain and aerosols in the form of fog Clouds consist of suspended droplets of water and ice its solid state When finely divided crystalline ice may precipitate in the form of snow The gaseous state of water is steam or water vapor Water covers about 71 of the Earth s surface with seas and oceans making up most of the water volume on earth about 96 5 4 Small portions of water occur as groundwater 1 7 in the glaciers and the ice caps of Antarctica and Greenland 1 7 and in the air as vapor clouds consisting of ice and liquid water suspended in air and precipitation 0 001 5 6 Water moves continually through the water cycle of evaporation transpiration evapotranspiration condensation precipitation and runoff usually reaching the sea Water plays an important role in the world economy Approximately 70 of the freshwater used by humans goes to agriculture 7 Fishing in salt and fresh water bodies has been and continues to be a major source of food for many parts of the world providing 6 5 of global protein 8 Much of the long distance trade of commodities such as oil natural gas and manufactured products is transported by boats through seas rivers lakes and canals Large quantities of water ice and steam are used for cooling and heating in industry and homes Water is an excellent solvent for a wide variety of substances both mineral and organic as such it is widely used in industrial processes and in cooking and washing Water ice and snow are also central to many sports and other forms of entertainment such as swimming pleasure boating boat racing surfing sport fishing diving ice skating and skiing Contents 1 Etymology 2 History 3 Properties 3 1 States 3 1 1 Density 3 1 2 Magnetism 3 1 3 Phase transitions 3 1 4 Triple and critical points 3 1 5 Phases of ice and water 3 2 Taste and odor 3 3 Color and appearance 3 4 Polar molecule 3 5 Hydrogen bonding 3 6 Self ionization 3 7 Electrical conductivity and electrolysis 3 8 Mechanical properties 3 9 Reactivity 4 On Earth 4 1 Water cycle 4 2 Water resources 4 3 Seawater and tides 5 Effects on life 5 1 Aquatic life forms 6 Effects on human civilization 6 1 Health and pollution 6 2 Human uses 6 2 1 Agriculture 6 2 2 As a scientific standard 6 2 3 For drinking 6 2 4 Washing 6 2 5 Transportation 6 2 6 Chemical uses 6 2 7 Heat exchange 6 2 8 Fire considerations 6 2 9 Recreation 6 2 10 Water industry 6 2 11 Industrial applications 6 2 12 Food processing 6 2 13 Medical use 7 Distribution in nature 7 1 In the universe 7 1 1 Water vapor 7 1 2 Liquid water 7 1 3 Water ice 7 1 4 Exotic forms 7 2 Water and planetary habitability 8 Law politics and crisis 9 In culture 9 1 Religion 9 2 Philosophy 9 3 Folklore 9 4 Art and activism 9 5 Dihydrogen monoxide parody 10 See also 11 Notes 12 References 12 1 Works cited 13 Further reading 14 External linksEtymologyThe word water comes from Old English waeter from Proto Germanic watar source also of Old Saxon watar Old Frisian wetir Dutch water Old High German wazzar German Wasser vatn Gothic 𐍅𐌰𐍄𐍉 wato from Proto Indo European wod or suffixed form of root wed water wet 9 Also cognate through the Indo European root with Greek ydwr ydor from Ancient Greek ὕdwr hydōr whence English hydro Russian voda voda Irish uisce and Albanian uje HistoryMain articles Origin of water on Earth History of water on Earth and Properties of water HistoryPropertiesMain article Properties of water See also Water data page and Water model A water molecule consists of two hydrogen atoms and one oxygen atom Water H2O is a polar inorganic compound At room temperature it is a tasteless and odorless liquid nearly colorless with a hint of blue This simplest hydrogen chalcogenide is by far the most studied chemical compound and is described as the universal solvent for its ability to dissolve many substances 10 11 This allows it to be the solvent of life 12 indeed water as found in nature almost always includes various dissolved substances and special steps are required to obtain chemically pure water Water is the only common substance to exist as a solid liquid and gas in normal terrestrial conditions 13 States The three common states of matter Along with oxidane water is one of the two official names for the chemical compound H2 O 14 it is also the liquid phase of H2 O 15 The other two common states of matter of water are the solid phase ice and the gaseous phase water vapor or steam The addition or removal of heat can cause phase transitions freezing water to ice melting ice to water vaporization water to vapor condensation vapor to water sublimation ice to vapor and deposition vapor to ice 16 Density See also Frost weathering Water differs from most liquids in that it becomes less dense as it freezes a In 1 atm pressure it reaches its maximum density of 999 972 kg m3 62 4262 lb cu ft at 3 98 C 39 16 F or almost 1 000 kg m3 62 43 lb cu ft at almost 4 C 39 F 18 19 The density of ice is 917 kg m3 57 25 lb cu ft an expansion of 9 20 21 This expansion can exert enormous pressure bursting pipes and cracking rocks 22 In a lake or ocean water at 4 C 39 F sinks to the bottom and ice forms on the surface floating on the liquid water This ice insulates the water below preventing it from freezing solid Without this protection most aquatic organisms residing in lakes would perish during the winter 23 Magnetism Water is a diamagnetic material 24 Though interaction is weak with superconducting magnets it can attain a notable interaction 24 Phase transitions At a pressure of one atmosphere atm ice melts or water freezes solidifies at 0 C 32 F and water boils or vapor condenses at 100 C 212 F However even below the boiling point water can change to vapor at its surface by evaporation vaporization throughout the liquid is known as boiling Sublimation and deposition also occur on surfaces 16 For example frost is deposited on cold surfaces while snowflakes form by deposition on an aerosol particle or ice nucleus 25 In the process of freeze drying a food is frozen and then stored at low pressure so the ice on its surface sublimates 26 The melting and boiling points depend on pressure A good approximation for the rate of change of the melting temperature with pressure is given by the Clausius Clapeyron relation d T d P T v L v S L f displaystyle frac dT dP frac T left v text L v text S right L text f where v L displaystyle v text L and v S displaystyle v text S are the molar volumes of the liquid and solid phases and L f displaystyle L text f is the molar latent heat of melting In most substances the volume increases when melting occurs so the melting temperature increases with pressure However because ice is less dense than water the melting temperature decreases 17 In glaciers pressure melting can occur under sufficiently thick volumes of ice resulting in subglacial lakes 27 28 The Clausius Clapeyron relation also applies to the boiling point but with the liquid gas transition the vapor phase has a much lower density than the liquid phase so the boiling point increases with pressure 29 Water can remain in a liquid state at high temperatures in the deep ocean or underground For example temperatures exceed 205 C 401 F in Old Faithful a geyser in Yellowstone National Park 30 In hydrothermal vents the temperature can exceed 400 C 752 F 31 At sea level the boiling point of water is 100 C 212 F As atmospheric pressure decreases with altitude the boiling point decreases by 1 C every 274 meters High altitude cooking takes longer than sea level cooking For example at 1 524 metres 5 000 ft cooking time must be increased by a fourth to achieve the desired result 32 Conversely a pressure cooker can be used to decrease cooking times by raising the boiling temperature 33 In a vacuum water will boil at room temperature 34 Triple and critical points Phase diagram of water simplified On a pressure temperature phase diagram see figure there are curves separating solid from vapor vapor from liquid and liquid from solid These meet at a single point called the triple point where all three phases can coexist The triple point is at a temperature of 273 16 K 0 01 C 32 02 F and a pressure of 611 657 pascals 0 00604 atm 0 0887 psi 35 it is the lowest pressure at which liquid water can exist Until 2019 the triple point was used to define the Kelvin temperature scale 36 37 The water vapor phase curve terminates at 647 096 K 373 946 C 705 103 F and 22 064 megapascals 3 200 1 psi 217 75 atm 38 This is known as the critical point At higher temperatures and pressures the liquid and vapor phases form a continuous phase called a supercritical fluid It can be gradually compressed or expanded between gas like and liquid like densities its properties which are quite different from those of ambient water are sensitive to density For example for suitable pressures and temperatures it can mix freely with nonpolar compounds including most organic compounds This makes it useful in a variety of applications including high temperature electrochemistry and as an ecologically benign solvent or catalyst in chemical reactions involving organic compounds In Earth s mantle it acts as a solvent during mineral formation dissolution and deposition 39 40 Phases of ice and water Main article Ice The normal form of ice on the surface of Earth is Ice Ih a phase that forms crystals with hexagonal symmetry Another with cubic crystalline symmetry Ice Ic can occur in the upper atmosphere 41 As the pressure increases ice forms other crystal structures As of 2019 17 have been experimentally confirmed and several more are predicted theoretically see Ice 42 The 18th form of ice ice XVIII a face centred cubic superionic ice phase was discovered when a droplet of water was subject to a shock wave that raised the water s pressure to millions of atmospheres and its temperature to thousands of degrees resulting in a structure of rigid oxygen atoms in which hydrogen atoms flowed freely 43 44 When sandwiched between layers of graphene ice forms a square lattice 45 The details of the chemical nature of liquid water are not well understood some theories suggest that its unusual behaviour is due to the existence of 2 liquid states 19 46 47 48 Taste and odor Pure water is usually described as tasteless and odorless although humans have specific sensors that can feel the presence of water in their mouths 49 50 and frogs are known to be able to smell it 51 However water from ordinary sources including bottled mineral water usually has many dissolved substances that may give it varying tastes and odors Humans and other animals have developed senses that enable them to evaluate the potability of water in order to avoid water that is too salty or putrid 52 Color and appearance Main article Color of water See also Electromagnetic absorption by water Pure water is visibly blue due to absorption of light in the region c 600 800 nm 53 The color can be easily observed in a glass of tap water placed against a pure white background in daylight The principal absorption bands responsible for the color are overtones of the O H stretching vibrations The apparent intensity of the color increases with the depth of the water column following Beer s law This also applies for example with a swimming pool when the light source is sunlight reflected from the pool s white tiles In nature the color may also be modified from blue to green due to the presence of suspended solids or algae In industry near infrared spectroscopy is used with aqueous solutions as the greater intensity of the lower overtones of water means that glass cuvettes with short path length may be employed To observe the fundamental stretching absorption spectrum of water or of an aqueous solution in the region around 3 500 cm 1 2 85 mm 54 a path length of about 25 mm is needed Also the cuvette must be both transparent around 3500 cm 1 and insoluble in water calcium fluoride is one material that is in common use for the cuvette windows with aqueous solutions The Raman active fundamental vibrations may be observed with for example a 1 cm sample cell Aquatic plants algae and other photosynthetic organisms can live in water up to hundreds of meters deep because sunlight can reach them Practically no sunlight reaches the parts of the oceans below 1 000 meters 3 300 ft of depth The refractive index of liquid water 1 333 at 20 C 68 F is much higher than that of air 1 0 similar to those of alkanes and ethanol but lower than those of glycerol 1 473 benzene 1 501 carbon disulfide 1 627 and common types of glass 1 4 to 1 6 The refraction index of ice 1 31 is lower than that of liquid water Polar molecule Tetrahedral structure of water In a water molecule the hydrogen atoms form a 104 5 angle with the oxygen atom The hydrogen atoms are close to two corners of a tetrahedron centered on the oxygen At the other two corners are lone pairs of valence electrons that do not participate in the bonding In a perfect tetrahedron the atoms would form a 109 5 angle but the repulsion between the lone pairs is greater than the repulsion between the hydrogen atoms 55 56 The O H bond length is about 0 096 nm 57 Other substances have a tetrahedral molecular structure for example methane CH4 and hydrogen sulfide H2 S However oxygen is more electronegative holds on to its electrons more tightly than most other elements so the oxygen atom retains a negative charge while the hydrogen atoms are positively charged Along with the bent structure this gives the molecule an electrical dipole moment and it is classified as a polar molecule 58 Water is a good polar solvent that dissolves many salts and hydrophilic organic molecules such as sugars and simple alcohols such as ethanol Water also dissolves many gases such as oxygen and carbon dioxide the latter giving the fizz of carbonated beverages sparkling wines and beers In addition many substances in living organisms such as proteins DNA and polysaccharides are dissolved in water The interactions between water and the subunits of these biomacromolecules shape protein folding DNA base pairing and other phenomena crucial to life hydrophobic effect Many organic substances such as fats and oils and alkanes are hydrophobic that is insoluble in water Many inorganic substances are insoluble too including most metal oxides sulfides and silicates Hydrogen bonding See also Chemical bonding of water Model of hydrogen bonds 1 between molecules of water Because of its polarity a molecule of water in the liquid or solid state can form up to four hydrogen bonds with neighboring molecules Hydrogen bonds are about ten times as strong as the Van der Waals force that attracts molecules to each other in most liquids This is the reason why the melting and boiling points of water are much higher than those of other analogous compounds like hydrogen sulfide They also explain its exceptionally high specific heat capacity about 4 2 J g K heat of fusion about 333 J g heat of vaporization 2257 J g and thermal conductivity between 0 561 and 0 679 W m K These properties make water more effective at moderating Earth s climate by storing heat and transporting it between the oceans and the atmosphere The hydrogen bonds of water are around 23 kJ mol compared to a covalent O H bond at 492 kJ mol Of this it is estimated that 90 is attributable to electrostatics while the remaining 10 is partially covalent 59 These bonds are the cause of water s high surface tension 60 and capillary forces The capillary action refers to the tendency of water to move up a narrow tube against the force of gravity This property is relied upon by all vascular plants such as trees citation needed Specific heat capacity of water 61 Self ionization Main article Self ionization of water Water is a weak solution of hydronium hydroxide there is an equilibrium 2H2 O H3 O OH in combination with solvation of the resulting hydronium ions Electrical conductivity and electrolysis Pure water has a low electrical conductivity which increases with the dissolution of a small amount of ionic material such as common salt Liquid water can be split into the elements hydrogen and oxygen by passing an electric current through it a process called electrolysis The decomposition requires more energy input than the heat released by the inverse process 285 8 kJ mol or 15 9 MJ kg 62 Mechanical properties Liquid water can be assumed to be incompressible for most purposes its compressibility ranges from 4 4 to 5 1 10 10 Pa 1 in ordinary conditions 63 Even in oceans at 4 km depth where the pressure is 400 atm water suffers only a 1 8 decrease in volume 64 The viscosity of water is about 10 3 Pa s or 0 01 poise at 20 C 68 F and the speed of sound in liquid water ranges between 1 400 and 1 540 meters per second 4 600 and 5 100 ft s depending on temperature Sound travels long distances in water with little attenuation especially at low frequencies roughly 0 03 dB km for 1 kHz a property that is exploited by cetaceans and humans for communication and environment sensing sonar 65 Reactivity Metallic elements which are more electropositive than hydrogen particularly the alkali metals and alkaline earth metals such as lithium sodium calcium potassium and cesium displace hydrogen from water forming hydroxides and releasing hydrogen At high temperatures carbon reacts with steam to form carbon monoxide and hydrogen On EarthMain articles Hydrology and Water distribution on Earth Hydrology is the study of the movement distribution and quality of water throughout the Earth The study of the distribution of water is hydrography The study of the distribution and movement of groundwater is hydrogeology of glaciers is glaciology of inland waters is limnology and distribution of oceans is oceanography Ecological processes with hydrology are in the focus of ecohydrology The collective mass of water found on under and over the surface of a planet is called the hydrosphere Earth s approximate water volume the total water supply of the world is 1 386 billion cubic kilometres 333 million cubic miles 5 Liquid water is found in bodies of water such as an ocean sea lake river stream canal pond or puddle The majority of water on Earth is seawater Water is also present in the atmosphere in solid liquid and vapor states It also exists as groundwater in aquifers Water is important in many geological processes Groundwater is present in most rocks and the pressure of this groundwater affects patterns of faulting Water in the mantle is responsible for the melt that produces volcanoes at subduction zones On the surface of the Earth water is important in both chemical and physical weathering processes Water and to a lesser but still significant extent ice are also responsible for a large amount of sediment transport that occurs on the surface of the earth Deposition of transported sediment forms many types of sedimentary rocks which make up the geologic record of Earth history Water cycle Main article Water cycle Water cycle The water cycle known scientifically as the hydrologic cycle is the continuous exchange of water within the hydrosphere between the atmosphere soil water surface water groundwater and plants Water moves perpetually through each of these regions in the water cycle consisting of the following transfer processes evaporation from oceans and other water bodies into the air and transpiration from land plants and animals into the air precipitation from water vapor condensing from the air and falling to the earth or ocean runoff from the land usually reaching the sea Most water vapors found mostly in the ocean returns to it but winds carry water vapor over land at the same rate as runoff into the sea about 47 Tt per year whilst evaporation and transpiration happening in land masses also contribute another 72 Tt per year Precipitation at a rate of 119 Tt per year over land has several forms most commonly rain snow and hail with some contribution from fog and dew 66 Dew is small drops of water that are condensed when a high density of water vapor meets a cool surface Dew usually forms in the morning when the temperature is the lowest just before sunrise and when the temperature of the earth s surface starts to increase 67 Condensed water in the air may also refract sunlight to produce rainbows Water runoff often collects over watersheds flowing into rivers Through erosion runoff shapes the environment creating river valleys and deltas which provide rich soil and level ground for the establishment of population centers A flood occurs when an area of land usually low lying is covered with water which occurs when a river overflows its banks or a storm surge happens On the other hand drought is an extended period of months or years when a region notes a deficiency in its water supply This occurs when a region receives consistently below average precipitation either due to its topography or due to its location in terms of latitude Water resources Main article Water resources Water resources are natural resources of water that are potentially useful for humans 68 for example as a source of drinking water supply or irrigation water Water occurs as both stocks and flows Water can be stored as lakes water vapor groundwater or aquifers and ice and snow Of the total volume of global freshwater an estimated 69 percent is stored in glaciers and permanent snow cover 30 percent is in groundwater and the remaining 1 percent in lakes rivers the atmosphere and biota 69 The length of time water remains in storage is highly variable some aquifers consist of water stored over thousands of years but lake volumes may fluctuate on a seasonal basis decreasing during dry periods and increasing during wet ones A substantial fraction of the water supply for some regions consists of water extracted from water stored in stocks and when withdrawals exceed recharge stocks decrease By some estimates as much as 30 percent of total water used for irrigation comes from unsustainable withdrawals of groundwater causing groundwater depletion 70 Seawater and tides Main articles Seawater and Tides Seawater contains about 3 5 sodium chloride on average plus smaller amounts of other substances The physical properties of seawater differ from fresh water in some important respects It freezes at a lower temperature about 1 9 C 28 6 F and its density increases with decreasing temperature to the freezing point instead of reaching maximum density at a temperature above freezing The salinity of water in major seas varies from about 0 7 in the Baltic Sea to 4 0 in the Red Sea The Dead Sea known for its ultra high salinity levels of between 30 and 40 is really a salt lake Tides are the cyclic rising and falling of local sea levels caused by the tidal forces of the Moon and the Sun acting on the oceans Tides cause changes in the depth of the marine and estuarine water bodies and produce oscillating currents known as tidal streams The changing tide produced at a given location is the result of the changing positions of the Moon and Sun relative to the Earth coupled with the effects of Earth rotation and the local bathymetry The strip of seashore that is submerged at high tide and exposed at low tide the intertidal zone is an important ecological product of ocean tides The Bay of Fundy at high tide and low tide High tide Low tideEffects on life Overview of photosynthesis green and respiration red From a biological standpoint water has many distinct properties that are critical for the proliferation of life It carries out this role by allowing organic compounds to react in ways that ultimately allow replication All known forms of life depend on water Water is vital both as a solvent in which many of the body s solutes dissolve and as an essential part of many metabolic processes within the body Metabolism is the sum total of anabolism and catabolism In anabolism water is removed from molecules through energy requiring enzymatic chemical reactions in order to grow larger molecules e g starches triglycerides and proteins for storage of fuels and information In catabolism water is used to break bonds in order to generate smaller molecules e g glucose fatty acids and amino acids to be used for fuels for energy use or other purposes Without water these particular metabolic processes could not exist Water is fundamental to photosynthesis and respiration Photosynthetic cells use the sun s energy to split off water s hydrogen from oxygen 71 Hydrogen is combined with CO2 absorbed from air or water to form glucose and release oxygen citation needed All living cells use such fuels and oxidize the hydrogen and carbon to capture the sun s energy and reform water and CO2 in the process cellular respiration Water is also central to acid base neutrality and enzyme function An acid a hydrogen ion H that is a proton donor can be neutralized by a base a proton acceptor such as a hydroxide ion OH to form water Water is considered to be neutral with a pH the negative log of the hydrogen ion concentration of 7 Acids have pH values less than 7 while bases have values greater than 7 Aquatic life forms Further information Hydrobiology Marine life and Aquatic plant Earth surface waters are filled with life The earliest life forms appeared in water nearly all fish live exclusively in water and there are many types of marine mammals such as dolphins and whales Some kinds of animals such as amphibians spend portions of their lives in water and portions on land Plants such as kelp and algae grow in the water and are the basis for some underwater ecosystems Plankton is generally the foundation of the ocean food chain Aquatic vertebrates must obtain oxygen to survive and they do so in various ways Fish have gills instead of lungs although some species of fish such as the lungfish have both Marine mammals such as dolphins whales otters and seals need to surface periodically to breathe air Some amphibians are able to absorb oxygen through their skin Invertebrates exhibit a wide range of modifications to survive in poorly oxygenated waters including breathing tubes see insect and mollusc siphons and gills Carcinus However as invertebrate life evolved in an aquatic habitat most have little or no specialization for respiration in water Some of the biodiversity of a coral reef Some marine diatoms a key phytoplankton group Squat lobster and Alvinocarididae shrimp at the Von Damm hydrothermal field survive by altered water chemistryEffects on human civilizationThis section needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed May 2018 Learn how and when to remove this template message Water fountain Civilization has historically flourished around rivers and major waterways Mesopotamia one of the so called cradles of civilization was situated between the major rivers Tigris and Euphrates the ancient society of the Egyptians depended entirely upon the Nile The early Indus Valley civilization c 3300 BCE to 1300 BCE developed along the Indus River and tributaries that flowed out of the Himalayas Rome was also founded on the banks of the Italian river Tiber Large metropolises like Rotterdam London Montreal Paris New York City Buenos Aires Shanghai Tokyo Chicago and Hong Kong owe their success in part to their easy accessibility via water and the resultant expansion of trade Islands with safe water ports like Singapore have flourished for the same reason In places such as North Africa and the Middle East where water is more scarce access to clean drinking water was and is a major factor in human development Health and pollution An environmental science program a student from Iowa State University sampling water Water fit for human consumption is called drinking water or potable water Water that is not potable may be made potable by filtration or distillation or by a range of other methods More than 660 million people do not have access to safe drinking water 72 73 Water that is not fit for drinking but is not harmful to humans when used for swimming or bathing is called by various names other than potable or drinking water and is sometimes called safe water or safe for bathing Chlorine is a skin and mucous membrane irritant that is used to make water safe for bathing or drinking Its use is highly technical and is usually monitored by government regulations typically 1 part per million ppm for drinking water and 1 2 ppm of chlorine not yet reacted with impurities for bathing water Water for bathing may be maintained in satisfactory microbiological condition using chemical disinfectants such as chlorine or ozone or by the use of ultraviolet light Water reclamation is the process of converting wastewater most commonly sewage also called municipal wastewater into water that can be reused for other purposes There are 2 3 billion people who reside in nations with water scarcities which means that each individual receives less than 1 700 cubic metres 60 000 cu ft of water annually 380 billion cubic metres 13 10 12 cu ft of municipal wastewater are produced globally each year 74 75 76 Freshwater is a renewable resource recirculated by the natural hydrologic cycle but pressures over access to it result from the naturally uneven distribution in space and time growing economic demands by agriculture and industry and rising populations Currently nearly a billion people around the world lack access to safe affordable water In 2000 the United Nations established the Millennium Development Goals for water to halve by 2015 the proportion of people worldwide without access to safe water and sanitation Progress toward that goal was uneven and in 2015 the UN committed to the Sustainable Development Goals of achieving universal access to safe and affordable water and sanitation by 2030 Poor water quality and bad sanitation are deadly some five million deaths a year are caused by water related diseases The World Health Organization estimates that safe water could prevent 1 4 million child deaths from diarrhoea each year 77 In developing countries 90 of all municipal wastewater still goes untreated into local rivers and streams 78 Some 50 countries with roughly a third of the world s population also suffer from medium or high water scarcity and 17 of these extract more water annually than is recharged through their natural water cycles 79 The strain not only affects surface freshwater bodies like rivers and lakes but it also degrades groundwater resources Human uses Further information Water supply Total water withdrawals for agricultural industrial and municipal purposes per capita measured in cubic metres m3 per year in 2010 80 Agriculture The most substantial human use of water is for agriculture including irrigated agriculture which accounts for as much as 80 to 90 percent of total human water consumption 81 In the United States 42 of freshwater withdrawn for use is for irrigation but the vast majority of water consumed used and not returned to the environment goes to agriculture 82 Access to fresh water is often taken for granted especially in developed countries that have built sophisticated water systems for collecting purifying and delivering water and removing wastewater But growing economic demographic and climatic pressures are increasing concerns about water issues leading to increasing competition for fixed water resources giving rise to the concept of peak water 83 As populations and economies continue to grow consumption of water thirsty meat expands and new demands rise for biofuels or new water intensive industries new water challenges are likely 84 An assessment of water management in agriculture was conducted in 2007 by the International Water Management Institute in Sri Lanka to see if the world had sufficient water to provide food for its growing population 85 It assessed the current availability of water for agriculture on a global scale and mapped out locations suffering from water scarcity It found that a fifth of the world s people more than 1 2 billion live in areas of physical water scarcity where there is not enough water to meet all demands A further 1 6 billion people live in areas experiencing economic water scarcity where the lack of investment in water or insufficient human capacity make it impossible for authorities to satisfy the demand for water The report found that it would be possible to produce the food required in the future but that continuation of today s food production and environmental trends would lead to crises in many parts of the world To avoid a global water crisis farmers will have to strive to increase productivity to meet growing demands for food while industries and cities find ways to use water more efficiently 86 Water scarcity is also caused by production of water intensive products For example cotton 1 kg of cotton equivalent of a pair of jeans requires 10 9 cubic meters 380 cu ft water to produce While cotton accounts for 2 4 of world water use the water is consumed in regions that are already at a risk of water shortage Significant environmental damage has been caused for example the diversion of water by the former Soviet Union from the Amu Darya and Syr Darya rivers to produce cotton was largely responsible for the disappearance of the Aral Sea 87 Water requirement per tonne of food product source source source source source source source source source source Water distribution in subsurface drip irrigation Irrigation of field cropsAs a scientific standard On 7 April 1795 the gram was defined in France to be equal to the absolute weight of a volume of pure water equal to a cube of one hundredth of a meter and at the temperature of melting ice 88 For practical purposes though a metallic reference standard was required one thousand times more massive the kilogram Work was therefore commissioned to determine precisely the mass of one liter of water In spite of the fact that the decreed definition of the gram specified water at 0 C 32 F a highly reproducible temperature the scientists chose to redefine the standard and to perform their measurements at the temperature of highest water density which was measured at the time as 4 C 39 F 89 The Kelvin temperature scale of the SI system was based on the triple point of water defined as exactly 273 16 K 0 01 C 32 02 F but as of May 2019 is based on the Boltzmann constant instead The scale is an absolute temperature scale with the same increment as the Celsius temperature scale which was originally defined according to the boiling point set to 100 C 212 F and melting point set to 0 C 32 F of water Natural water consists mainly of the isotopes hydrogen 1 and oxygen 16 but there is also a small quantity of heavier isotopes oxygen 18 oxygen 17 and hydrogen 2 deuterium The percentage of the heavier isotopes is very small but it still affects the properties of water Water from rivers and lakes tends to contain less heavy isotopes than seawater Therefore standard water is defined in the Vienna Standard Mean Ocean Water specification For drinking Main article Drinking water A young girl drinking bottled water Water availability the fraction of the population using improved water sources by country Roadside fresh water outlet from glacier Nubra The human body contains from 55 to 78 water depending on body size 90 user generated source To function properly the body requires between one and seven liters 0 22 and 1 54 imp gal 0 26 and 1 85 U S gal citation needed of water per day to avoid dehydration the precise amount depends on the level of activity temperature humidity and other factors Most of this is ingested through foods or beverages other than drinking straight water It is not clear how much water intake is needed by healthy people though the British Dietetic Association advises that 2 5 liters of total water daily is the minimum to maintain proper hydration including 1 8 liters 6 to 7 glasses obtained directly from beverages 91 Medical literature favors a lower consumption typically 1 liter of water for an average male excluding extra requirements due to fluid loss from exercise or warm weather 92 Healthy kidneys can excrete 0 8 to 1 liter of water per hour but stress such as exercise can reduce this amount People can drink far more water than necessary while exercising putting them at risk of water intoxication hyperhydration which can be fatal 93 94 The popular claim that a person should consume eight glasses of water per day seems to have no real basis in science 95 Studies have shown that extra water intake especially up to 500 milliliters 18 imp fl oz 17 U S fl oz at mealtime was associated with weight loss 96 97 98 99 100 101 Adequate fluid intake is helpful in preventing constipation 102 Hazard symbol for non potable water An original recommendation for water intake in 1945 by the Food and Nutrition Board of the U S National Research Council read An ordinary standard for diverse persons is 1 milliliter for each calorie of food Most of this quantity is contained in prepared foods 103 The latest dietary reference intake report by the U S National Research Council in general recommended based on the median total water intake from US survey data including food sources 3 7 liters 0 81 imp gal 0 98 U S gal for men and 2 7 liters 0 59 imp gal 0 71 U S gal of water total for women noting that water contained in food provided approximately 19 of total water intake in the survey 104 Specifically pregnant and breastfeeding women need additional fluids to stay hydrated The US Institute of Medicine recommends that on average men consume 3 liters 0 66 imp gal 0 79 U S gal and women 2 2 liters 0 48 imp gal 0 58 U S gal pregnant women should increase intake to 2 4 liters 0 53 imp gal 0 63 U S gal and breastfeeding women should get 3 liters 12 cups since an especially large amount of fluid is lost during nursing 105 Also noted is that normally about 20 of water intake comes from food while the rest comes from drinking water and beverages caffeinated included Water is excreted from the body in multiple forms through urine and feces through sweating and by exhalation of water vapor in the breath With physical exertion and heat exposure water loss will increase and daily fluid needs may increase as well Humans require water with few impurities Common impurities include metal salts and oxides including copper iron calcium and lead 106 full citation needed and or harmful bacteria such as Vibrio Some solutes are acceptable and even desirable for taste enhancement and to provide needed electrolytes 107 The single largest by volume freshwater resource suitable for drinking is Lake Baikal in Siberia 108 Washing This section is an excerpt from Washing edit A woman washes her hands with soap and water Washing is a method of cleaning usually with water and soap or detergent Washing and then rinsing both body and clothing is an essential part of good hygiene and health citation needed Often people use soaps and detergents to assist in the emulsification of oils and dirt particles so they can be washed away The soap can be applied directly or with the aid of a washcloth People wash themselves or bathe periodically for religious ritual or therapeutic purposes 109 or as a recreational activity In Europe some people use a bidet to wash their external genitalia and the anal region after using the toilet instead of using toilet paper 110 The bidet is common in predominantly Catholic countries where water is considered essential for anal cleansing 111 More frequent is washing of just the hands e g before and after preparing food and eating after using the toilet after handling something dirty etc Hand washing is important in reducing the spread of germs 112 113 114 Also common is washing the face which is done after waking up or to keep oneself cool during the day Brushing one s teeth is also essential for hygiene and is a part of washing Washing can also refer to the washing of clothing or other cloth items like bedsheets whether by hand or with a washing machine It can also refer to washing one s car by lathering the exterior with car soap then rinsing it off with a hose or washing cookware A private home washing machine Excessive washing may damage the hair causing dandruff or cause rough skin skin lesions 115 116 Transportation These paragraphs are an excerpt from Maritime transport edit Maritime transport or ocean transport or more generally waterborne transport is the transport of people passengers or goods cargo via waterways Freight transport by sea has been widely used throughout recorded history The advent of aviation has diminished the importance of sea travel for passengers though it is still popular for short trips and pleasure cruises Transport by water is cheaper than transport by air 117 despite fluctuating exchange rates and a fee placed on top of freighting charges for carrier companies known as the currency adjustment factor Maritime transport accounts for roughly 80 of international trade according to UNCTAD in 2020 Maritime transport can be realized over any distance by boat ship sailboat or barge over oceans and lakes through canals or along rivers Shipping may be for commerce recreation or military purposes While extensive inland shipping is less critical today the major waterways of the world including many canals are still very important and are integral parts of worldwide economies Particularly especially any material can be moved by water however water transport becomes impractical when material delivery is time critical such as various types of perishable produce Still water transport is highly cost effective with regular schedulable cargoes such as trans oceanic shipping of consumer products and especially for heavy loads or bulk cargos such as coal coke ores or grains Arguably the industrial revolution took place best where cheap water transport by canal navigations or shipping by all types of watercraft on natural waterways supported cost effective bulk transport Containerization revolutionized maritime transport starting in the 1970s General cargo includes goods packaged in boxes cases pallets and barrels When a cargo is carried in more than one mode it is intermodal or co modal Chemical uses Water is widely used in chemical reactions as a solvent or reactant and less commonly as a solute or catalyst In inorganic reactions water is a common solvent dissolving many ionic compounds as well as other polar compounds such as ammonia and compounds closely related to water In organic reactions it is not usually used as a reaction solvent because it does not dissolve the reactants well and is amphoteric acidic and basic and nucleophilic Nevertheless these properties are sometimes desirable Also acceleration of Diels Alder reactions by water has been observed Supercritical water has recently been a topic of research Oxygen saturated supercritical water combusts organic pollutants efficiently Heat exchange Water and steam are a common fluid used for heat exchange due to its availability and high heat capacity both for cooling and heating Cool water may even be naturally available from a lake or the sea It is especially effective to transport heat through vaporization and condensation of water because of its large latent heat of vaporization A disadvantage is that metals commonly found in industries such as steel and copper are oxidized faster by untreated water and steam In almost all thermal power stations water is used as the working fluid used in a closed loop between boiler steam turbine and condenser and the coolant used to exchange the waste heat to a water body or carry it away by evaporation in a cooling tower In the United States cooling power plants is the largest use of water 118 In the nuclear power industry water can also be used as a neutron moderator In most nuclear reactors water is both a coolant and a moderator This provides something of a passive safety measure as removing the water from the reactor also slows the nuclear reaction down However other methods are favored for stopping a reaction and it is preferred to keep the nuclear core covered with water so as to ensure adequate cooling Fire considerations Water is used for fighting wildfires Water has a high heat of vaporization and is relatively inert which makes it a good fire extinguishing fluid The evaporation of water carries heat away from the fire It is dangerous to use water on fires involving oils and organic solvents because many organic materials float on water and the water tends to spread the burning liquid Use of water in fire fighting should also take into account the hazards of a steam explosion which may occur when water is used on very hot fires in confined spaces and of a hydrogen explosion when substances which react with water such as certain metals or hot carbon such as coal charcoal or coke graphite decompose the water producing water gas The power of such explosions was seen in the Chernobyl disaster although the water involved in this case did not come from fire fighting but from the reactor s own water cooling system A steam explosion occurred when the extreme overheating of the core caused water to flash into steam A hydrogen explosion may have occurred as a result of a reaction between steam and hot zirconium Some metallic oxides most notably those of alkali metals and alkaline earth metals produce so much heat on reaction with water that a fire hazard can develop The alkaline earth oxide quicklime is a mass produced substance that is often transported in paper bags If these are soaked through they may ignite as their contents react with water 119 Recreation Main article Water sport recreation San Andres island Colombia Humans use water for many recreational purposes as well as for exercising and for sports Some of these include swimming waterskiing boating surfing and diving In addition some sports like ice hockey and ice skating are played on ice Lakesides beaches and water parks are popular places for people to go to relax and enjoy recreation Many find the sound and appearance of flowing water to be calming and fountains and other flowing water structures are popular decorations Some keep fish and other flora and fauna inside aquariums or ponds for show fun and companionship Humans also use water for snow sports such as skiing sledding snowmobiling or snowboarding which the require the water to be at a low temperature either as ice or crystallized into snow Water industry The water industry provides drinking water and wastewater services including sewage treatment to households and industry Water supply facilities include water wells cisterns for rainwater harvesting water supply networks and water purification facilities water tanks water towers water pipes including old aqueducts Atmospheric water generators are in development Drinking water is often collected at springs extracted from artificial borings wells in the ground or pumped from lakes and rivers Building more wells in adequate places is thus a possible way to produce more water assuming the aquifers can supply an adequate flow Other water sources include rainwater collection Water may require purification for human consumption This may involve the removal of undissolved substances dissolved substances and harmful microbes Popular methods are filtering with sand which only removes undissolved material while chlorination and boiling kill harmful microbes Distillation does all three functions More advanced techniques exist such as reverse osmosis Desalination of abundant seawater is a more expensive solution used in coastal arid climates The distribution of drinking water is done through municipal water systems tanker delivery or as bottled water Governments in many countries have programs to distribute water to the needy at no charge Reducing usage by using drinking potable water only for human consumption is another option In some cities such as Hong Kong seawater is extensively used for flushing toilets citywide in order to conserve freshwater resources Polluting water may be the biggest single misuse of water to the extent that a pollutant limits other uses of the water it becomes a waste of the resource regardless of benefits to the polluter Like other types of pollution this does not enter standard accounting of market costs being conceived as externalities for which the market cannot account Thus other people pay the price of water pollution while the private firms profits are not redistributed to the local population victims of this pollution Pharmaceuticals consumed by humans often end up in the waterways and can have detrimental effects on aquatic life if they bioaccumulate and if they are not biodegradable Municipal and industrial wastewater are typically treated at wastewater treatment plants Mitigation of polluted surface runoff is addressed through a variety of prevention and treatment techniques See Surface runoff Mitigation and treatment A water carrier in India 1882 In many places where running water is not available water has to be transported by people A manual water pump in China Water purification facility Reverse osmosis RO desalination plant in Barcelona Spain Industrial applications Many industrial processes rely on reactions using chemicals dissolved in water suspension of solids in water slurries or using water to dissolve and extract substances or to wash products or process equipment Processes such as mining chemical pulping pulp bleaching paper manufacturing textile production dyeing printing and cooling of power plants use large amounts of water requiring a dedicated water source and often cause significant water pollution Water is used in power generation Hydroelectricity is electricity obtained from hydropower Hydroelectric power comes from water driving a water turbine connected to a generator Hydroelectricity is a low cost non polluting renewable energy source The energy is supplied by the motion of water Typically a dam is constructed on a river creating an artificial lake behind it Water flowing out of the lake is forced through turbines that turn generators Three Gorges Dam is the largest hydro electric power station in the world Pressurized water is used in water blasting and water jet cutters Also high pressure water guns are used for precise cutting It works very well is relatively safe and is not harmful to the environment It is also used in the cooling of machinery to prevent overheating or prevent saw blades from overheating Water is also used in many industrial processes and machines such as the steam turbine and heat exchanger in addition to its use as a chemical solvent Discharge of untreated water from industrial uses is pollution Pollution includes discharged solutes chemical pollution and discharged coolant water thermal pollution Industry requires pure water for many applications and uses a variety of purification techniques both in water supply and discharge Food processing Water can be used to cook foods such as noodles Sterile water for injection Boiling steaming and simmering are popular cooking methods that often require immersing food in water or its gaseous state steam 120 Water is also used for dishwashing Water also plays many critical roles within the field of food science Solutes such as salts and sugars found in water affect the physical properties of water The boiling and freezing points of water are affected by solutes as well as air pressure which is in turn affected by altitude Water boils at lower temperatures with the lower air pressure that occurs at higher elevations One mole of sucrose sugar per kilogram of water raises the boiling point of water by 0 51 C 0 918 F and one mole of salt per kg raises the boiling point by 1 02 C 1 836 F similarly increasing the number of dissolved particles lowers water s freezing point 121 Solutes in water also affect water activity that affects many chemical reactions and the growth of microbes in food 122 Water activity can be described as a ratio of the vapor pressure of water in a solution to the vapor pressure of pure water 121 Solutes in water lower water activity this is important to know because most bacterial growth ceases at low levels of water activity 122 Not only does microbial growth affect the safety of food but also the preservation and shelf life of food Water hardness is also a critical factor in food processing and may be altered or treated by using a chemical ion exchange system It can dramatically affect the quality of a product as well as playing a role in sanitation Water hardness is classified based on concentration of calcium carbonate the water contains Water is classified as soft if it contains less than 100 mg L UK 123 or less than 60 mg L US 124 According to a report published by the Water Footprint organization in 2010 a single kilogram of beef requires 15 thousand liters 3 3 10 3 imp gal 4 0 10 3 U S gal of water however the authors also make clear that this is a global average and circumstantial factors determine the amount of water used in beef production 125 Medical use Water for injection is on the World Health Organization s list of essential medicines 126 Distribution in natureIn the universe Band 5 ALMA receiver is an instrument specifically designed to detect water in the universe 127 Much of the universe s water is produced as a byproduct of star formation The formation of stars is accompanied by a strong outward wind of gas and dust When this outflow of material eventually impacts the surrounding gas the shock waves that are created compress and heat the gas The water observed is quickly produced in this warm dense gas 128 On 22 July 2011 a report described the discovery of a gigantic cloud of water vapor containing 140 trillion times more water than all of Earth s oceans combined around a quasar located 12 billion light years from Earth According to the researchers the discovery shows that water has been prevalent in the universe for nearly its entire existence 129 130 Water has been detected in interstellar clouds within the Milky Way 131 Water probably exists in abundance in other galaxies too because its components hydrogen and oxygen are among the most abundant elements in the universe Based on models of the formation and evolution of the Solar System and that of other star systems most other planetary systems are likely to have similar ingredients Water vapor Water is present as vapor in Atmosphere of the Sun in detectable trace amounts 132 Atmosphere of Mercury 3 4 and large amounts of water in Mercury s exosphere 133 Atmosphere of Venus 0 002 134 Earth s atmosphere 0 40 over full atmosphere typically 1 4 at surface as well as that of the Moon in trace amounts 135 Atmosphere of Mars 0 03 136 Atmosphere of Ceres 137 Atmosphere of Jupiter 0 0004 138 in ices only and that of its moon Europa 139 Atmosphere of Saturn in ices only Enceladus 91 140 and Dione exosphere citation needed Atmosphere of Uranus in trace amounts below 50 bar Atmosphere of Neptune found in the deeper layers 141 Extrasolar planet atmospheres including those of HD 189733 b 142 and HD 209458 b 143 Tau Bootis b 144 HAT P 11b 145 146 XO 1b WASP 12b WASP 17b and WASP 19b 147 Stellar atmospheres not limited to cooler stars and even detected in giant hot stars such as Betelgeuse Mu Cephei Antares and Arcturus 146 148 Circumstellar disks including those of more than half of T Tauri stars such as AA Tauri 146 as well as TW Hydrae 149 150 IRC 10216 151 and APM 08279 5255 129 130 VY Canis Majoris and S Persei 148 Liquid water Liquid water is present on Earth covering 71 of its surface 4 Liquid water is also occasionally present in small amounts on Mars 152 Scientists believe liquid water is present in the Saturnian moons of Enceladus as a 10 kilometre thick ocean approximately 30 40 kilometres below Enceladus south polar surface 153 154 and Titan as a subsurface layer possibly mixed with ammonia 155 Jupiter s moon Europa has surface characteristics which suggest a subsurface liquid water ocean 156 Liquid water may also exist on Jupiter s moon Ganymede as a layer sandwiched between high pressure ice and rock 157 Water ice Water is present as ice on South polar ice cap of Mars during Martian south summer 2000 Mars under the regolith and at the poles 158 159 Earth Moon system mainly as ice sheets on Earth and in Lunar craters and volcanic rocks 160 NASA reported the detection of water molecules by NASA s Moon Mineralogy Mapper aboard the Indian Space Research Organization s Chandrayaan 1 spacecraft in September 2009 161 Ceres 162 163 164 Jupiter s moons Europa s surface and also that of Ganymede 165 and Callisto 166 167 Saturn in the planet s ring system 168 and on the surface and mantle of Titan 169 and Enceladus 170 Pluto Charon system 168 Comets 171 172 and other related Kuiper belt and Oort cloud objects 173 And is also likely present on Mercury s poles 174 Tethys 175 Exotic forms Water and other volatiles probably comprise much of the internal structures of Uranus and Neptune and the water in the deeper layers may be in the form of ionic water in which the molecules break down into a soup of hydrogen and oxygen ions and deeper still as superionic water in which the oxygen crystallizes but the hydrogen ions float about freely within the oxygen lattice 176 Water and planetary habitability Further information Water distribution on Earth and Planetary habitability The existence of liquid water and to a lesser extent its gaseous and solid forms on Earth are vital to the existence of life on Earth as we know it The Earth is located in the habitable zone of the Solar System if it were slightly closer to or farther from the Sun about 5 or about 8 million kilometers the conditions which allow the three forms to be present simultaneously would be far less likely to exist 177 178 Earth s gravity allows it to hold an atmosphere Water vapor and carbon dioxide in the atmosphere provide a temperature buffer greenhouse effect which helps maintain a relatively steady surface temperature If Earth were smaller a thinner atmosphere would allow temperature extremes thus preventing the accumulation of water except in polar ice caps as on Mars citation needed The surface temperature of Earth has been relatively constant through geologic time despite varying levels of incoming solar radiation insolation indicating that a dynamic process governs Earth s temperature via a combination of greenhouse gases and surface or atmospheric albedo This proposal is known as the Gaia hypothesis citation needed The state of water on a planet depends on ambient pressure which is determined by the planet s gravity If a planet is sufficiently massive the water on it may be solid even at high temperatures because of the high pressure caused by gravity as it was observed on exoplanets Gliese 436 b 179 and GJ 1214 b 180 Law politics and crisisMain articles Water law Water right and Water crisis This section needs to be updated Please help update this article to reflect recent events or newly available information June 2022 An estimate of the proportion of people in developing countries with access to potable water 1970 2000 Water politics is politics affected by water and water resources Water particularly fresh water is a strategic resource across the world and an important element in many political conflicts It causes health impacts and damage to biodiversity Access to safe drinking water has improved over the last decades in almost every part of the world but approximately one billion people still lack access to safe water and over 2 5 billion lack access to adequate sanitation 181 However some observers have estimated that by 2025 more than half of the world population will be facing water based vulnerability 182 A report issued in November 2009 suggests that by 2030 in some developing regions of the world water demand will exceed supply by 50 183 1 6 billion people have gained access to a safe water source since 1990 184 The proportion of people in developing countries with access to safe water is calculated to have improved from 30 in 1970 185 to 71 in 1990 79 in 2000 and 84 in 2004 181 A 2006 United Nations report stated that there is enough water for everyone but that access to it is hampered by mismanagement and corruption 186 In addition global initiatives to improve the efficiency of aid delivery such as the Paris Declaration on Aid Effectiveness have not been taken up by water sector donors as effectively as they have in education and health potentially leaving multiple donors working on overlapping projects and recipient governments without empowerment to act 187 The authors of the 2007 Comprehensive Assessment of Water Management in Agriculture cited poor governance as one reason for some forms of water scarcity Water governance is the set of formal and informal processes through which decisions related to water management are made Good water governance is primarily about knowing what processes work best in a particular physical and socioeconomic context Mistakes have sometimes been made by trying to apply blueprints that work in the developed world to developing world locations and contexts The Mekong river is one example a review by the International Water Management Institute of policies in six countries that rely on the Mekong river for water found that thorough and transparent cost benefit analyses and environmental impact assessments were rarely undertaken They also discovered that Cambodia s draft water law was much more complex than it needed to be 188 The UN World Water Development Report WWDR 2003 from the World Water Assessment Program indicates that in the next 20 years the quantity of water available to everyone is predicted to decrease by 30 40 of the world s inhabitants currently have insufficient fresh water for minimal hygiene More than 2 2 million people died in 2000 from waterborne diseases related to the consumption of contaminated water or drought In 2004 the UK charity WaterAid reported that a child dies every 15 seconds from easily preventable water related diseases often this means lack of sewage disposal citation needed Organizations concerned with water protection include the International Water Association IWA WaterAid Water 1st and the American Water Resources Association The International Water Management Institute undertakes projects with the aim of using effective water management to reduce poverty Water related conventions are United Nations Convention to Combat Desertification UNCCD International Convention for the Prevention of Pollution from Ships United Nations Convention on the Law of the Sea and Ramsar Convention World Day for Water takes place on 22 March 189 and World Oceans Day on 8 June 190 In cultureReligion Main article Water and religion See also Sacred waters People come to Inda Abba Hadera spring Inda Sillasie Ethiopia to wash in holy water Water is considered a purifier in most religions Faiths that incorporate ritual washing ablution include Christianity 191 Hinduism Islam Judaism the Rastafari movement Shinto Taoism and Wicca Immersion or aspersion or affusion of a person in water is a central Sacrament of Christianity where it is called baptism it is also a part of the practice of other religions including Islam Ghusl Judaism mikvah and Sikhism Amrit Sanskar In addition a ritual bath in pure water is performed for the dead in many religions including Islam and Judaism In Islam the five daily prayers can be done in most cases after washing certain parts of the body using clean water wudu unless water is unavailable see Tayammum In Shinto water is used in almost all rituals to cleanse a person or an area e g in the ritual of misogi In Christianity holy water is water that has been sanctified by a priest for the purpose of baptism the blessing of persons places and objects or as a means of repelling evil 192 193 In Zoroastrianism water ab is respected as the source of life 194 Philosophy Icosahedron as a part of Spinoza monument in Amsterdam The Ancient Greek philosopher Empedocles saw water as one of the four classical elements along with fire earth and air and regarded it as an ylem or basic substance of the universe Thales whom Aristotle portrayed as an astronomer and an engineer theorized that the earth which is denser than water emerged from the water Thales a monist believed further that all things are made from water Plato believed that the shape of water is an icosahedron flowing easily compared to the cube shaped earth 195 The theory of the four bodily humors associated water with phlegm as being cold and moist The classical element of water was also one of the five elements in traditional Chinese philosophy along with earth fire wood and metal Some traditional and popular Asian philosophical systems take water as a role model James Legge s 1891 translation of the Dao De Jing states The highest excellence is like that of water The excellence of water appears in its benefiting all things and in its occupying without striving to the contrary the low place which all men dislike Hence its way is near to that of the Tao and There is nothing in the world more soft and weak than water and yet for attacking things that are firm and strong there is nothing that can take precedence of it for there is nothing so effectual for which it can be changed 196 Guanzi in the Shui di 水地 chapter further elaborates on the symbolism of water proclaiming that man is water and attributing natural qualities of the people of different Chinese regions to the character of local water resources 197 Folklore Living water features in Germanic and Slavic folktales as a means of bringing the dead back to life Note the Grimm fairy tale The Water of Life and the Russian dichotomy of living ru and dead water ru The Fountain of Youth represents a related concept of magical waters allegedly preventing aging Art and activism Painter and activist Fredericka Foster curated The Value of Water at the Cathedral of St John the Divine in New York City 198 which anchored a year long initiative by the Cathedral on our dependence on water 199 200 The largest exhibition to ever appear at the Cathedral 201 it featured over forty artists including Jenny Holzer Robert Longo Mark Rothko William Kentridge April Gornik Kiki Smith Pat Steir William Kentridge Alice Dalton Brown Teresita Fernandez and Bill Viola 202 203 Foster created Think About Water 204 full citation needed an ecological collective of artists who use water as their subject or medium Members include Basia Irland 205 full citation needed Aviva Rahmani Betsy Damon Diane Burko Leila Daw Stacy Levy Charlotte Cote 206 Meridel Rubenstein Stacy Levy Anna Macleod and Aviva Rahmani To mark the 10th anniversary of access to water and sanitation being declared a human right by the UN the charity WaterAid commissioned ten visual artists to show the impact of clean water on people s lives 207 208 Dihydrogen monoxide parody Main article Dihydrogen monoxide parody Water s technically correct but rarely used chemical name dihydrogen monoxide has been used in a series of hoaxes and pranks that mock scientific illiteracy This began in 1983 when an April Fools Day article appeared in a newspaper in Durand Michigan The false story consisted of safety concerns about the substance 209 See also Water portalOutline of water Overview of and topical guide to water Water data page Chemical data page for water is a collection of the chemical and physical properties of water Aquaphobia Persistent and abnormal fear of water Human right to water and sanitation Human right recognized by the United Nations General Assembly in 2010 Mpemba effect Natural phenomenon that hot water freezes faster than cold Oral rehydration therapy Type of fluid replacement used to prevent and treat dehydration Thirst Craving for potable fluids experienced by animals Water pinch 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Stanley Supercooled and Glassy Water Physics Today 56 6 pp 40 46 2003 Downloadable PDF 1 9 MB Archived 1 November 2018 at the Wayback Machine Gleick PH editor The World s Water The Biennial Report on Freshwater Resources Island Press Washington D C published every two years beginning in 1998 The World s Water Island Press Archived 26 February 2009 at the Wayback Machine Jones Oliver A Lester John N Voulvoulis Nick 2005 Pharmaceuticals a threat to drinking water Trends in Biotechnology 23 4 163 167 doi 10 1016 j tibtech 2005 02 001 PMID 15780706 Journal of Contemporary Water Research amp Education Archived 3 March 2016 at the Wayback Machine Postel S Last Oasis Facing Water Scarcity W W Norton and Company New York 1992 Reisner M Cadillac Desert The American West and Its Disappearing Water Penguin Books New York 1986 United Nations World Water Development Report Archived 22 February 2009 at the Wayback Machine Produced every three years St Fleur Nicholas The Water in Your Glass Might Be Older Than the Sun Archived 15 January 2017 at the Wayback Machine The water you drink is older than the planet you re standing on The New York Times 15 April 2016 External linkswater at Wikipedia s sister projects Definitions from Wiktionary Media from Commons News from Wikinews Quotations from Wikiquote Texts from Wikisource Textbooks from Wikibooks Resources from Wikiversity OECD Water statistics The World s Water Data Page FAO Comprehensive Water Database AQUASTAT The Water Conflict Chronology Water Conflict Database Archived 16 January 2013 at the Wayback Machine Water science school USGS Portal to The World Bank s strategy work and associated publications on water resources America Water Resources Association Archived 24 March 2018 at the Wayback Machine Water on the web Water structure and science Archived 28 December 2014 at the Wayback Machine Why water is one of the weirdest things in the universe Ideas BBC Video 3 16 minutes 2019 The chemistry of water Archived 19 June 2020 at the Wayback Machine NSF special report The International Association for the Properties of Water and Steam H2O The Molecule That Made Us a 2020 PBS documentary Retrieved from https en wikipedia org w index php title Water amp oldid 1139190160, wikipedia, wiki, book, books, library,

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