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Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's
hydrosphere The hydrosphere () is the combined mass of water found on, under, and above the surface of a planet, minor planet, or natural satellite. Although Earth's hydrosphere has been around for about 4 billion years, it continues to change in shape. This ...
and the fluids of all known living organisms (in which it acts as a solvent). 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 Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-to ...
atoms, connected by covalent bonds. The hydrogen atoms are attached to the oxygen atom at an angle of 104.45°. "Water" is also the name of the liquid state of H2O at standard temperature and pressure. A number of natural states of water exist. It forms
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
in the form of rain and aerosols in the form of
fog Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influ ...
. 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%). Small portions of water occur as
groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit ...
(1.7%), in the glaciers and the
ice caps In glaciology, an ice cap is a mass of ice that covers less than of land area (usually covering a highland area). Larger ice masses covering more than are termed ice sheets. Description Ice caps are not constrained by topographical features ...
of Antarctica and Greenland (1.7%), and in the air as vapor, clouds (consisting of ice and liquid water suspended in air), and
precipitation In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
(0.001%). Water moves continually through the
water cycle The water cycle, also known as the hydrologic cycle or the hydrological cycle, is a biogeochemical cycle that describes the continuous movement of water on, above and below the surface of the Earth. The mass of water on Earth remains fairly co ...
of evaporation, transpiration ( evapotranspiration), condensation, precipitation, and
runoff Runoff, run-off or RUNOFF may refer to: * RUNOFF, the first computer text-formatting program * Runoff or run-off, another name for bleed, printing that lies beyond the edges to which a printed sheet is trimmed * Runoff or run-off, a stock marke ...
, usually reaching the sea. Water plays an important role in the world economy. Approximately 70% of the freshwater used by
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goes to agriculture. 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. 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 Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlers in the mid-5th ...
, from
Proto-Germanic Proto-Germanic (abbreviated PGmc; also called Common Germanic) is the reconstructed proto-language of the Germanic branch of the Indo-European languages. Proto-Germanic eventually developed from pre-Proto-Germanic into three Germanic br ...
*''watar'' (source also of Old Saxon , Old Frisian , Dutch ,
Old High German Old High German (OHG; german: Althochdeutsch (Ahd.)) is the earliest stage of the German language, conventionally covering the period from around 750 to 1050. There is no standardised or supra-regional form of German at this period, and Old Hig ...
,
German German(s) may refer to: * Germany (of or related to) **Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...
, ,
Gothic Gothic or Gothics may refer to: People and languages *Goths or Gothic people, the ethnonym of a group of East Germanic tribes **Gothic language, an extinct East Germanic language spoken by the Goths **Crimean Gothic, the Gothic language spoken b ...
(), from Proto-Indo-European *''wod-or'', suffixed form of root *''wed-'' ("water"; "wet"). Also cognate, through the Indo-European root, with Greek (, from Ancient Greek , ''hýdōr,'' whence English "hydro-"), Russian (), Irish , and Albanian .


History


Properties

Water () is a
polar Polar may refer to: Geography Polar may refer to: * Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates *Polar climate, the cli ...
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. This allows it to be the " solvent of life": indeed, water as found in nature almost always includes various dissolved substances, and special steps are required to obtain chemically
pure water Purified water is water that has been mechanically filtered or processed to remove impurities and make it suitable for use. Distilled water was, formerly, the most common form of purified water, but, in recent years, water is more frequently puri ...
. Water is the only common substance to exist as a solid, liquid, and gas in normal terrestrial conditions.


States

Along with ''oxidane'', ''water'' is one of the two official names for the chemical compound ; it is also the liquid phase of . 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 Deposition may refer to: * Deposition (law), taking testimony outside of court * Deposition (politics), the removal of a person of authority from political power * Deposition (university), a widespread initiation ritual for new students practiced f ...
(vapor to ice).


Density

Water differs from most liquids in that it becomes less dense as it freezes. In 1 atm pressure, it reaches its maximum density of at , or almost at almost . The density of ice is , an expansion of 9%. This expansion can exert enormous pressure, bursting pipes and cracking rocks. In a lake or ocean, water at 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.


Magnetism

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


Phase transitions

At a pressure of one atmosphere (atm), ice melts or water freezes (solidifies) at ) and water boils or vapor condenses at . 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. For example, frost is deposited on cold surfaces while snowflakes form by deposition on an aerosol particle or ice nucleus. In the process of freeze-drying, a food is frozen and then stored at low pressure so the ice on its surface sublimates. 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: \frac = \frac, where v_\text and v_\text are the molar volumes of the liquid and solid phases, and L_\text 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. In glaciers, pressure melting can occur under sufficiently thick volumes of ice, resulting in subglacial lakes. 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. Water can remain in a liquid state at high temperatures in the deep ocean or underground. For example, temperatures exceed in Old Faithful, a geyser in Yellowstone National Park. In hydrothermal vents, the temperature can exceed . At sea level, the boiling point of water is . 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 , cooking time must be increased by a fourth to achieve the desired result. (Conversely, a
pressure cooker Pressure cooking is the process of cooking food under high pressure steam and water or a water-based cooking liquid, in a sealed vessel known as a ''pressure cooker''. High pressure limits boiling, and creates higher cooking temperatures whic ...
can be used to decrease cooking times by raising the boiling temperature.) In a vacuum, water will boil at room temperature.


Triple and critical points

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 In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.. It is that temperature and pressure at which the ...
, where all three phases can coexist. The triple point is at a temperature of and a pressure of ; it is the lowest pressure at which liquid water can exist. Until 2019, the triple point was used to define the
Kelvin temperature scale The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and p ...
. The water/vapor phase curve terminates at and . 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.


Phases of ice and water

The normal form of ice on the surface of Earth is
Ice Ih Photograph showing details of an ice cube under magnification. Ice Ih is the form of ice commonly seen on Earth. Phase space of ice Ih with respect to other ice phases. Ice Ih (hexagonal ice crystal) (pronounced: ice one h, also known as ice-p ...
, a phase that forms crystals with hexagonal symmetry. Another with cubic crystalline symmetry,
Ice Ic Ice Ic (pronounced "ice one c" or "ice I see") is a metastable cubic crystalline variant of ice. Hans König was the first to identify and deduce the structure of ice Ic. The oxygen atoms in ice Ic are arranged in a diamond structure; it is ...
, can occur in the upper atmosphere. As the pressure increases, ice forms other
crystal structure In crystallography, crystal structure is a description of the ordered arrangement of atoms, ions or molecules in a crystalline material. Ordered structures occur from the intrinsic nature of the constituent particles to form symmetric pattern ...
s. As of 2019, 17 have been experimentally confirmed and several more are predicted theoretically (see Ice). 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. When sandwiched between layers of graphene, ice forms a square lattice. 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.


Taste and odor

Pure water is usually described as tasteless and odorless, although
humans" \n\n\n\n\nThe robots exclusion standard, also known as the robots exclusion protocol or simply robots.txt, is a standard used by websites to indicate to visiting web crawlers and other web robots which portions of the site they are allowed to visi ...
have specific sensors that can feel the presence of water in their mouths,Edmund T. Rolls (2005). ''Emotion Explained''. Oxford University Press, Medical. , 9780198570035. and frogs are known to be able to smell it.R. Llinas, W. Precht (2012), ''Frog Neurobiology: A Handbook''. Springer Science & Business Media. , 9783642663161 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.


Color and appearance

Pure water is visibly blue due to
absorption Absorption may refer to: Chemistry and biology *Absorption (biology), digestion **Absorption (small intestine) *Absorption (chemistry), diffusion of particles of gas or liquid into liquid or solid materials *Absorption (skin), a route by which s ...
of light in the region c. 600–800 nm. 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 (2.85 μm) a path length of about 25 μm is needed. Also, the cuvette must be both transparent around 3500 cm 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 of depth. The refractive index of liquid water (1.333 at ) 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

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. The O–H bond length is about 0.096 nm. Other substances have a tetrahedral molecular structure, for example,
methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The relative abundance of methane ...
() and hydrogen sulfide (). However, oxygen is more
electronegative Electronegativity, symbolized as , is the tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond. An atom's electronegativity is affected by both its atomic number and the ...
(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. 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
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, res ...
s, 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 In nutrition, biology, and chemistry, fat usually means any ester of fatty acids, or a mixture of such compounds, most commonly those that occur in living beings or in food. The term often refers specifically to triglycerides (triple est ...
and
alkanes In organic chemistry, an alkane, or paraffin (a historical trivial name that also has other meanings), is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a tree structure in ...
) are hydrophobic, that is, insoluble in water. Many inorganic substances are insoluble too, including most metal oxides, sulfides, and silicates.


Hydrogen bonding

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 In thermodynamics, the enthalpy of fusion of a substance, also known as (latent) heat of fusion, is the change in its enthalpy resulting from providing energy, typically heat, to a specific quantity of the substance to change its state from a s ...
(about 333 J/g), heat of vaporization (), and
thermal conductivity The thermal conductivity of a material is a measure of its ability to conduct heat. It is commonly denoted by k, \lambda, or \kappa. Heat transfer occurs at a lower rate in materials of low thermal conductivity than in materials of high thermal ...
(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. These bonds are the cause of water's high surface tension 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.


Self-ionization

Water is a weak solution of hydronium hydroxide – there is an equilibrium ⇔ + , in combination with solvation of the resulting
hydronium In chemistry, hydronium (hydroxonium in traditional British English) is the common name for the aqueous cation , the type of oxonium ion produced by protonation of water. It is often viewed as the positive ion present when an Arrhenius acid ...
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).


Mechanical properties

Liquid water can be assumed to be incompressible for most purposes: its compressibility ranges from 4.4 to in ordinary conditions. Even in oceans at 4 km depth, where the pressure is 400 atm, water suffers only a 1.8% decrease in volume. The viscosity of water is about 10 Pa· s or 0.01 poise at , and the speed of sound in liquid water ranges between depending on temperature. Sound travels long distances in water with little attenuation, especially at low frequencies (roughly 0.03 dB/km for 1 k Hz), a property that is exploited by cetaceans and humans for communication and environment sensing (
sonar Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances (ranging), communicate with or detect objects on o ...
).UK National Physical Laboratory
Calculation of absorption of sound in seawater
. Online site, last accessed on 28 September 2016.


Reactivity

Metallic elements which are more electropositive than hydrogen, particularly the alkali metals and alkaline earth metals such as lithium, sodium,
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar ...
, 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

Hydrology is the study of the movement, distribution, and quality of water throughout the Earth. The study of the distribution of water is
hydrography Hydrography is the branch of applied sciences which deals with the measurement and description of the physical features of oceans, seas, coastal areas, lakes and rivers, as well as with the prediction of their change over time, for the prima ...
. The study of the distribution and movement of
groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available freshwater in the world is groundwater. A unit ...
is hydrogeology, of glaciers is glaciology, of inland waters is
limnology Limnology ( ; from Greek λίμνη, ''limne'', "lake" and λόγος, ''logos'', "knowledge") is the study of inland aquatic ecosystems. The study of limnology includes aspects of the biological, chemical, physical, and geological characteris ...
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 The hydrosphere () is the combined mass of water found on, under, and above the surface of a planet, minor planet, or natural satellite. Although Earth's hydrosphere has been around for about 4 billion years, it continues to change in shape. This ...
. Earth's approximate water volume (the total water supply of the world) is . Liquid water is found in bodies of water, such as an ocean, sea, lake, river, stream,
canal Canals or artificial waterways are waterways or engineered channels built for drainage management (e.g. flood control and irrigation) or for conveyancing water transport vehicles (e.g. water taxi). They carry free, calm surface f ...
, 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 A mantle is a piece of clothing, a type of cloak. Several other meanings are derived from that. Mantle may refer to: *Mantle (clothing), a cloak-like garment worn mainly by women as fashionable outerwear **Mantle (vesture), an Eastern Orthodox ve ...
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 Deposition may refer to: * Deposition (law), taking testimony outside of court * Deposition (politics), the removal of a person of authority from political power * Deposition (university), a widespread initiation ritual for new students practiced f ...
of transported sediment forms many types of sedimentary rocks, which make up the geologic record of
Earth history The history of Earth concerns the development of planet Earth from its formation to the present day. Nearly all branches of natural science have contributed to understanding of the main events of Earth's past, characterized by constant geologi ...
.


Water cycle

The water cycle (known scientifically as the hydrologic cycle) is the continuous exchange of water within the
hydrosphere The hydrosphere () is the combined mass of water found on, under, and above the surface of a planet, minor planet, or natural satellite. Although Earth's hydrosphere has been around for about 4 billion years, it continues to change in shape. This ...
, 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 In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls under gravitational pull from clouds. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. ...
, from water vapor condensing from the air and falling to the earth or ocean. *
runoff Runoff, run-off or RUNOFF may refer to: * RUNOFF, the first computer text-formatting program * Runoff or run-off, another name for bleed, printing that lies beyond the edges to which a printed sheet is trimmed * Runoff or run-off, a stock marke ...
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 Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influ ...
and dew. 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. Condensed water in the air may also
refract In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomeno ...
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

Water resources are natural resources of water that are potentially useful for humans, 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. 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.


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 ) 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.


Effects on life

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. Hydrogen is combined with (absorbed from air or water) to form glucose and release oxygen. All living cells use such fuels and oxidize the hydrogen and carbon to capture the sun's energy and reform water and in the process (cellular respiration). Water is also central to acid-base neutrality and enzyme function. An acid, a hydrogen ion (, that is, a proton) donor, can be neutralized by a base, a proton acceptor such as a hydroxide ion () 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

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 Seals may refer to: * Pinniped, a diverse group of semi-aquatic marine mammals, many of which are commonly called seals, particularly: ** Earless seal, or "true seal" ** Fur seal * Seal (emblem), a device to impress an emblem, used as a means of a ...
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

Civilization has historically flourished around rivers and major waterways; Mesopotamia, one of the so-called
cradles of civilization A cradle of civilization is a location and a culture where civilization was created by mankind independent of other civilizations in other locations. The formation of urban settlements (cities) is the primary characteristic of a society that c ...
, 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 Rotterdam ( , , , lit. ''The Dam on the River Rotte (river), Rotte'') is the second largest List of cities in the Netherlands by province, city and List of municipalities of the Netherlands, municipality in the Netherlands. It is in the Prov ...
,
London London is the capital and List of urban areas in the United Kingdom, largest city of England and the United Kingdom, with a population of just under 9 million. It stands on the River Thames in south-east England at the head of a estuary dow ...
,
Montreal Montreal ( ; officially Montréal, ) is the second-most populous city in Canada and most populous city in the Canadian province of Quebec. Founded in 1642 as '' Ville-Marie'', or "City of Mary", it is named after Mount Royal, the triple- ...
, Paris,
New York City New York, often called New York City or NYC, is the List of United States cities by population, most populous city in the United States. With a 2020 population of 8,804,190 distributed over , New York City is also the L ...
, Buenos Aires,
Shanghai Shanghai (; , , Standard Chinese, Standard Mandarin pronunciation: ) is one of the four Direct-administered municipalities of China, direct-administered municipalities of the China, People's Republic of China (PRC). The city is located on the ...
,
Tokyo Tokyo (; ja, 東京, , ), officially the Tokyo Metropolis ( ja, 東京都, label=none, ), is the capital and largest city of Japan. Formerly known as Edo, its metropolitan area () is the most populous in the world, with an estimated 37.46 ...
,
Chicago (''City in a Garden''); I Will , image_map = , map_caption = Interactive Map of Chicago , coordinates = , coordinates_footnotes = , subdivision_type = List of sovereign states, Count ...
, and
Hong Kong Hong Kong ( (US) or (UK); , ), officially the Hong Kong Special Administrative Region of the People's Republic of China (abbr. Hong Kong SAR or HKSAR), is a List of cities in China, city and Special administrative regions of China, special ...
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

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. 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 of water annually. of municipal wastewater are produced globally each year. 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 Diarrhea, also spelled diarrhoea, is the condition of having at least three loose, liquid, or watery bowel movements each day. It often lasts for a few days and can result in dehydration due to fluid loss. Signs of dehydration often begin w ...
each year. In developing countries, 90% of all municipal wastewater still goes untreated into local rivers and streams. 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. The strain not only affects surface freshwater bodies like rivers and lakes, but it also degrades groundwater resources.


Human uses


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. 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. 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. 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. An assessment of water management in agriculture was conducted in 2007 by the
International Water Management Institute The International Water Management Institute (IWMI) is a non-profit international water management research organisation under the CGIAR with its headquarters in Colombo, Sri Lanka, and offices across Africa and Asia. Research at the Institute foc ...
in Sri Lanka to see if the world had sufficient water to provide food for its growing population. 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. 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 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 The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen nationa ...
from the Amu Darya and Syr Darya rivers to produce cotton was largely responsible for the disappearance of the Aral Sea. File:Water requirement per tonne of food product, OWID.svg, Water requirement per tonne of food product File:Subsurface drip emission on loamy soil.ogv, Water distribution in subsurface drip irrigation File:SiphonTubes.JPG, 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". 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 —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 . The
Kelvin temperature scale The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and p ...
of the SI system was based on the
triple point In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.. It is that temperature and pressure at which the ...
of water, defined as exactly , but as of May 2019 is based on the
Boltzmann constant The Boltzmann constant ( or ) is the proportionality factor that relates the average relative kinetic energy of particles in a gas with the thermodynamic temperature of the gas. It occurs in the definitions of the kelvin and the gas constan ...
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 ) and melting point (set to ) 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

The human body contains from 55% to 78% water, depending on body size. To function properly, the body requires between 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. 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. 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 Water intoxication, also known as water poisoning, hyperhydration, overhydration, or water toxemia, is a potentially fatal disturbance in brain functions that results when the normal balance of electrolytes in the body is pushed outside safe l ...
(hyperhydration), which can be fatal. The popular claim that "a person should consume eight glasses of water per day" seems to have no real basis in science. Studies have shown that extra water intake, especially up to at mealtime, was associated with weight loss. Adequate fluid intake is helpful in preventing constipation. An original recommendation for water intake in 1945 by the Food and Nutrition Board of the
U.S. National Research Council The National Academies of Sciences, Engineering, and Medicine (also known as NASEM or the National Academies) are the collective scientific national academy of the United States. The name is used interchangeably in two senses: (1) as an umbrell ...
read: "An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods." 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): for men and of water total for women, noting that water contained in food provided approximately 19% of total water intake in the survey. Specifically, pregnant and breastfeeding women need additional fluids to stay hydrated. The US Institute of Medicine recommends that, on average, men consume and women ; pregnant women should increase intake to and breastfeeding women should get 3 liters (12 cups), since an especially large amount of fluid is lost during nursing. Also noted is that normally, about 20% of water intake comes from food, while the rest comes from drinking water and beverages (
caffeinated Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is mainly used recreationally as a cognitive enhancer, increasing alertness and attentional performance. Caffeine acts by blocking binding of adenosine t ...
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, and/or harmful bacteria, such as '' Vibrio''. Some
solutes In chemistry, a solution is a special type of homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. If the attractive forces between the solven ...
are acceptable and even desirable for taste enhancement and to provide needed electrolytes. The single largest (by volume) freshwater resource suitable for drinking is Lake Baikal in Siberia.


Washing


Transportation


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 Supercritical water oxidation (SCWO) is a process that occurs in water at temperatures and pressures above a mixture's thermodynamic critical point. Under these conditions water becomes a fluid with unique properties that can be used to advantag ...
has recently been a topic of research. Oxygen-saturated supercritical water combusts organic pollutants efficiently. Water vapor is used for some processes in the chemical industry. An example is the production of acrylic acid from acrolein, propylene and propane. The possible effect of water in these reactions includes the physical and chemical interaction of water with the catalyst and the chemical reaction of water with the reaction intermediates.


Heat exchange

Water and steam are a common fluid used for heat exchange, due to its availability and high
heat capacity Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to an object to produce a unit change in its temperature. The SI unit of heat capacity is joule per kelvin (J/K). Heat cap ...
, 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 Redox (reduction–oxidation, , ) is a type of chemical reaction in which the oxidation states of substrate change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is the gain of electrons or a ...
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."Water Use in the United States"
''National Atlas''.
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 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.


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 Sledding, sledging or sleighing is a winter sport typically carried out in a prone or seated position on a vehicle generically known as a sled (North American), a sledge (British), or a sleigh. It is the basis of three Olympic sports: luge, ske ...
,
snowmobiling A snowmobile, also known as a Ski-Doo, snowmachine, sled, motor sled, motor sledge, skimobile, or snow scooter, is a motorized vehicle designed for winter travel and recreation on snow. It is designed to be operated on snow and ice and does not ...
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 network A water supply network or water supply system is a system of engineered hydrologic and hydraulic components that provide water supply. A water supply system typically includes the following: # A drainage basin (see water purification – sou ...
s, 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 system A water supply network or water supply system is a system of engineered hydrologic and hydraulic components that provide water supply. A water supply system typically includes the following: # A drainage basin (see water purification – source ...
s, 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 In economics, an externality or external cost is an indirect cost or benefit to an uninvolved third party that arises as an effect of another party's (or parties') activity. Externalities can be considered as unpriced goods involved in either c ...
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 Paper chemicals designate a group of chemicals that are used for paper manufacturing, or modify the properties of paper. These chemicals can be used to alter the paper in many ways, including changing its color and brightness, or by increasing i ...
, 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 Hydropower (from el, ὕδωρ, "water"), also known as water power, is the use of falling or fast-running water to produce electricity or to power machines. This is achieved by converting the gravitational potential or kinetic energy of ...
. 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. 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 is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, th ...
. 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

Boiling,
steaming Steaming is a method of cooking using steam. This is often done with a food steamer, a kitchen appliance made specifically to cook food with steam, but food can also be steamed in a wok. In the American southwest, steam pits used for cooking ha ...
, and simmering are popular cooking methods that often require immersing food in water or its gaseous state, steam. Water is also used for dishwashing. Water also plays many critical roles within the field of food science.
Solutes In chemistry, a solution is a special type of homogeneous mixture composed of two or more substances. In such a mixture, a solute is a substance dissolved in another substance, known as a solvent. If the attractive forces between the solven ...
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 , and one mole of salt per kg raises the boiling point by ; similarly, increasing the number of dissolved particles lowers water's freezing point. Solutes in water also affect water activity that affects many chemical reactions and the growth of microbes in food. Water activity can be described as a ratio of the vapor pressure of water in a solution to the vapor pressure of pure water. Solutes in water lower water activity—this is important to know because most bacterial growth ceases at low levels of water activity. Not only does microbial growth affect the safety of food, but also the preservation and shelf life of food.
Water hardness Hard water is water that has high mineral content (in contrast with "soft water"). Hard water is formed when water percolates through deposits of limestone, chalk or gypsum, which are largely made up of calcium and magnesium carbonates, bica ...
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) or less than 60 mg/L (US). According to a report published by the Water Footprint organization in 2010, a single kilogram of beef requires 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.


Medical use

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


Distribution in nature


In the universe

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. 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". Water has been detected in
interstellar cloud An interstellar cloud is generally an accumulation of gas, plasma, and dust in our and other galaxies. Put differently, an interstellar cloud is a denser-than-average region of the interstellar medium, the matter and radiation that exists in the ...
s within the Milky Way. 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 * Atmosphere of Mercury: 3.4%, and large amounts of water in Mercury's exosphere * Atmosphere of Venus: 0.002% * Earth's atmosphere: ≈0.40% over full atmosphere, typically 1–4% at surface; as well as that of the Moon in trace amounts * Atmosphere of Mars: 0.03% *
Atmosphere of Ceres Ceres (; minor-planet designation: 1 Ceres) is a dwarf planet in the asteroid belt between the orbits of Mars and Jupiter. It was the first asteroid discovered, on 1 January 1801, by Giuseppe Piazzi at Palermo Astronomical Observatory in Sici ...
* Atmosphere of Jupiter: 0.0004% – in ices only; and that of its moon
Europa Europa may refer to: Places * Europe * Europa (Roman province), a province within the Diocese of Thrace * Europa (Seville Metro), Seville, Spain; a station on the Seville Metro * Europa City, Paris, France; a planned development * Europa Clif ...
* Atmosphere of Saturn – in ices only; Enceladus: 91% and Dione (exosphere) * Atmosphere of Uranus – in trace amounts below 50 bar * Atmosphere of Neptune – found in the deeper layers * Extrasolar planet atmospheres: including those of HD 189733 b and HD 209458 b,Water Found in Extrasolar Planet's Atmosphere
– Space.com
Tau Boötis b, HAT-P-11b, XO-1b, WASP-12b, WASP-17b, and WASP-19b. * Stellar atmospheres: not limited to cooler stars and even detected in giant hot stars such as Betelgeuse, Mu Cephei, Antares and Arcturus.Andersson, Jonas (June 2012)
Water in stellar atmospheres "Is a novel picture required to explain the atmospheric behavior of water in red giant stars?"
Lund Observatory, Lund University, Sweden
* Circumstellar disks: including those of more than half of T Tauri stars such as
AA Tauri AA Tauri is a young variable star in the equatorial constellation of Taurus, located in the Taurus-Auriga star-forming region. It is too faint to view with the naked eye, having an apparent visual magnitude that varies from 12.2 do ...
as well as
TW Hydrae TW Hydrae is a T Tauri star approximately 196 light-years away in the constellation of Hydra (the Sea Serpent). TW Hydrae is about 80% of the mass of the Sun, but is only about 5-10 million years old. The star appears to be accreting fro ...
,
IRC +10216 CW Leonis or IRC +10216 is a carbon star that is embedded in a thick dust envelope. It was first discovered in 1969 by a group of astronomers led by Eric Becklin, based upon infrared observations made with the Caltech Infrared Telescope ...
and APM 08279+5255, VY Canis Majoris and
S Persei S Persei is a red supergiant or hypergiant located near the Double Cluster in Perseus, north of the cluster NGC 869. It is a member of the Perseus OB1 association and one of the largest known stars. If placed in the Solar System, its ...
.


Liquid water

Liquid water is present on Earth, covering 71% of its surface. Liquid water is also occasionally present in small amounts on Mars. 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, and
Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...
, as a subsurface layer, possibly mixed with ammonia. Jupiter's moon
Europa Europa may refer to: Places * Europe * Europa (Roman province), a province within the Diocese of Thrace * Europa (Seville Metro), Seville, Spain; a station on the Seville Metro * Europa City, Paris, France; a planned development * Europa Clif ...
has surface characteristics which suggest a subsurface liquid water ocean. Liquid water may also exist on Jupiter's moon Ganymede as a layer sandwiched between high pressure ice and rock.


Water ice

Water is present as ice on: * Mars: under the regolith and at the poles. * Earth–Moon system: mainly as ice sheets on Earth and in Lunar craters and volcanic rocks 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. * Ceres * Jupiter's moons:
Europa Europa may refer to: Places * Europe * Europa (Roman province), a province within the Diocese of Thrace * Europa (Seville Metro), Seville, Spain; a station on the Seville Metro * Europa City, Paris, France; a planned development * Europa Clif ...
's surface and also that of Ganymede and Callisto * Saturn: in the planet's ring system and on the surface and mantle of
Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictiona ...
and Enceladus (supporting online material, table S1) *
Pluto Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of trans-Neptunian object, bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the S ...
Charon system * Comets and other related Kuiper belt and Oort cloud objects And is also likely present on: * Mercury's poles * Tethys


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 Superionic water, also called superionic ice or ice XVIII is a phase of water that exists at extremely high temperatures and pressures. In superionic water, water molecules break apart and the oxygen ions crystallize into an evenly spaced lat ...
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.Weird water lurking inside giant planets
, ''New Scientist'', 1 September 2010, Magazine issue 2776.


Water 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. 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 cap A polar ice cap or polar cap is a high-latitude region of a planet, dwarf planet, or natural satellite that is covered in ice. There are no requirements with respect to size or composition for a body of ice to be termed a polar ice cap, no ...
s (as on Mars). 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. 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 and GJ 1214 b.


Law, politics, and crisis

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. However, some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in some developing regions of the world, water demand will exceed supply by 50%. 1.6 billion people have gained access to a safe water source since 1990. The proportion of people in developing countries with access to safe water is calculated to have improved from 30% in 1970 to 71% in 1990, 79% in 2000, and 84% in 2004. A 2006 United Nations report stated that "there is enough water for everyone", but that access to it is hampered by mismanagement and corruption. 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. The authors of the 2007
Comprehensive Assessment of Water Management in Agriculture The report ''A Comprehensive Assessment of Water Management in Agriculture'' was published in 2007 by International Water Management Institute and Earthscan in an attempt to answer the question: how can water in agriculture be developed and manage ...
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 The International Water Management Institute (IWMI) is a non-profit international water management research organisation under the CGIAR with its headquarters in Colombo, Sri Lanka, and offices across Africa and Asia. Research at the Institute foc ...
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. The UN World Water Development Report (WWDR, 2003) from the
World Water Assessment Program The UNESCO World Water Assessment Programme (UNESCO WWAP) was founded in 2000 in response to a call from the UN Commission on Sustainable Development (CSD) to produce a UN system-wide periodic global overview of the status (quantity and quality), u ...
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. Organizations concerned with water protection include the International Water Association (IWA), WaterAid,
Water 1st Water 1st International is a non-profit organization whose stated goal is helping people in poor countries implement water, sanitation and hygiene education projects. Water 1st works through locally based partner organizations to support the impl ...
, and the American Water Resources Association. The
International Water Management Institute The International Water Management Institute (IWMI) is a non-profit international water management research organisation under the CGIAR with its headquarters in Colombo, Sri Lanka, and offices across Africa and Asia. Research at the Institute foc ...
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 World Water Day is an annual United Nations (UN) observance day held on 22 March that highlights the importance of fresh water. The day is used to advocate for the sustainable management of freshwater resources. The theme of each year focuses ...
takes place on 22 March and World Oceans Day on 8 June.


In culture


Religion

Water is considered a purifier in most religions. Faiths that incorporate ritual washing (
ablution Ablution is the act of washing oneself. It may refer to: * Ablution as hygiene * Ablution as ritual purification ** Ablution in Islam: *** Wudu, daily wash *** Ghusl, bathing ablution *** Tayammum, waterless ablution ** Ablution in Christianity ...
) include
Christianity Christianity is an Abrahamic monotheistic religion based on the life and teachings of Jesus of Nazareth. It is the world's largest and most widespread religion with roughly 2.38 billion followers representing one-third of the global popula ...
, Hinduism,
Islam Islam (; ar, ۘالِإسلَام, , ) is an Abrahamic monotheistic religion centred primarily around the Quran, a religious text considered by Muslims to be the direct word of God (or '' Allah'') as it was revealed to Muhammad, the ...
, Judaism, the Rastafari movement,
Shinto Shinto () is a religion from Japan. Classified as an East Asian religion by scholars of religion, its practitioners often regard it as Japan's indigenous religion and as a nature religion. Scholars sometimes call its practitioners ''Shint ...
, 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 Sikhism (), also known as Sikhi ( pa, ਸਿੱਖੀ ', , from pa, ਸਿੱਖ, lit=disciple', 'seeker', or 'learner, translit=Sikh, label=none),''Sikhism'' (commonly known as ''Sikhī'') originated from the word ''Sikh'', which comes fro ...
(''
Amrit Sanskar Amrit Sanchar (Gurmukhi: ਅੰਮ੍ਰਿਤ ਸੰਸਕਾਰ "nectar ceremony"; also called Amrit Parchar, or Khande di Pahul ਖੰਡੇ ਦੀ ਪਾਹੁਲ) is one of the four Sikh Sanskaars. The Amrit Sanskar is the initiation rite ...
''). 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 In religion, a blessing (also used to refer to bestowing of such) is the impartation of something with grace, holiness, spiritual redemption, or divine will. Etymology and Germanic paganism The modern English language term ''bless'' likely ...
of persons, places, and objects, or as a means of repelling evil. In Zoroastrianism, water ('' āb'') is respected as the source of life.


Philosophy

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 Ylem ( or ) is a hypothetical original substance or condensed state of matter, which became subatomic particles and elements as we understand them today. The term was used by George Gamow, his student Ralph Alpher, and their associates in the la ...
, 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 Monism attributes oneness or singleness (Greek: μόνος) to a concept e.g., existence. Various kinds of monism can be distinguished: * Priority monism states that all existing things go back to a source that is distinct from them; e.g., i ...
, 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. The theory of the four bodily humors associated water with
phlegm Phlegm (; , ''phlégma'', "inflammation", " humour caused by heat") is mucus produced by the respiratory system, excluding that produced by the nasal passages. It often refers to respiratory mucus expelled by coughing, otherwise known as sput ...
, 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 A metal (from ancient Greek, Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electrical resistivity and conductivity, e ...
). 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." '' 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.


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 and . 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 The Cathedral of St. John the Divine (sometimes referred to as St. John's and also nicknamed St. John the Unfinished) is the cathedral of the Episcopal Diocese of New York. It is at 1047 Amsterdam Avenue in the Morningside Heights neighborhood ...
in New York City, which anchored a year-long initiative by the Cathedral on our dependence on water. The largest exhibition to ever appear at the Cathedral, it featured over forty artists, including Jenny Holzer, Robert Longo, Mark Rothko,
William Kentridge William Kentridge (born 28 April 1955) is a South African artist best known for his prints, drawings, and animated films, especially noted for a sequence of hand-drawn animated films he produced during the 1990s. The latter are constructed by ...
,
April Gornik : April Gornik (born 1953, Cleveland, Ohio) is an American artist who paints American landscapes. Her realist yet dreamlike paintings and drawings embody oppositions and speak to America's historically conflicted relationship with nature. While ...
, Kiki Smith,
Pat Steir Pat Steir (born 1940) is an American painter and printmaker. Her early work was loosely associated with conceptual art and minimalism, however, she is best known for her abstract dripped, splashed and poured "Waterfall" paintings, which she sta ...
,
William Kentridge William Kentridge (born 28 April 1955) is a South African artist best known for his prints, drawings, and animated films, especially noted for a sequence of hand-drawn animated films he produced during the 1990s. The latter are constructed by ...
,
Alice Dalton Brown Alice Dalton Brown (born 1939) is an American painter known for realist works that capture the light and texture of specific, if often invented, places and moments.Henry, Gerrit. "Alice Dalton Brown," ''ARTnews'', November 1983, p. 207.Kingsle ...
,
Teresita Fernandez Teresita may refer to: * Teresita (given name), a feminine given name * ''Teresita'' (genus), a genus of moths in the family Oecophoridae * Teresita, Missouri, United States, an unincorporated community * Teresita, Oklahoma, United States, an u ...
and Bill Viola. Foster created Think About Water, an ecological collective of artists who use water as their subject or medium. Members include Basia Irland, Aviva Rahmani, Betsy Damon,
Diane Burko Diane Burko (born 1945 Brooklyn, NY) is an American painter and photographer. She is currently based in Philadelphia and Bucks County, Pennsylvania. Her work addresses landscape, climate change and environmental activism. Biography Diane B ...
,
Leila Daw Leila Daw (born 1940) is an American installation artist and art professor; her work uses diverse materials to explore themes of cartography and feminism. Life and work Leila Daw received her Masters of Fine Arts from the St. Louis School of Fi ...
,
Stacy Levy Stacy Levy (born 1960) is a sculptor who works with ecological natural patterns and processes, often using water and water flows as a medium. Many of her works address environmental problems at the same time that they make the functioning of th ...
, Charlotte Coté,
Meridel Rubenstein Meridel Rubenstein (born 1948) is an American photographer and installation artist based out of New Mexico. She is known for her large-format photographs incorporating sculptures and unusual media. Biography Rubenstein was born in Detroit, Mic ...
,
Stacy Levy Stacy Levy (born 1960) is a sculptor who works with ecological natural patterns and processes, often using water and water flows as a medium. Many of her works address environmental problems at the same time that they make the functioning of th ...
,
Anna Macleod Anna MacGillivray Macleod DSc (15 May 1917 – 13 August 2004) was a Scottish biochemist and academic, an authority on brewing and distilling. She was a professor at Heriot-Watt University in Edinburgh. She was the world's first female Professo ...
, 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.


Dihydrogen monoxide parody

Water's technically correct but rarely used
chemical name A chemical nomenclature is a set of rules to generate systematic names for chemical compounds. The nomenclature used most frequently worldwide is the one created and developed by the International Union of Pure and Applied Chemistry (IUPAC). The ...
, dihydrogen monoxide, has been used in a series of hoaxes and pranks that mock
scientific illiteracy Scientific literacy or science literacy encompasses written, numerical, and digital literacy as they pertain to understanding science, its methodology, observations, and theories. Scientific literacy is chiefly concerned with an understanding of ...
. 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.


See also

* * is a collection of the chemical and physical properties of water. * (fear of water) * * * * *


Notes


References


Works cited

* *


Further reading

* Debenedetti, PG., and HE Stanley, "Supercooled and Glassy Water", ''Physics Today'' 56 (6), pp. 40–46 (2003)
Downloadable PDF (1.9 MB)
* 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
*
Journal of Contemporary Water Research & Education
* 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
. Produced every three years. * St. Fleur, Nicholas

. "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



Water science school
(USGS)
Portal to The World Bank's strategy, work and associated publications on water resources

America Water Resources Association

Water on the web

Water structure and science

"Why water is one of the weirdest things in the universe"
''Ideas'', BBC, Video, 3:16 minutes, 2019
The chemistry of water
(NSF special report)

* ttps://www.pbs.org/wgbh/molecule-that-made-us ''H2O: The Molecule That Made Us'' a 2020 PBS documentary {{Authority control Articles containing video clips Hydrogen compounds Inorganic solvents Liquids Materials that expand upon freezing Nuclear reactor coolants Oxides Oxygen compounds