Water

Water

Oxygen, O   Hydrogen, H
Names
IUPAC name Water
Systematic IUPAC name Oxidane
Other names Hydrogen oxide Hydrogen hydroxide (HH or HOH) Hydroxylic acid Dihydrogen monoxide (DHMO) (parody name[1]) Dihydrogen oxide Hydric acid Hydrohydroxic acid Hydroxic acid Hydroxoic acid Hydrol[2] μ-Oxidodihydrogen κ1-Hydroxylhydrogen(0) Aqua Neutral liquid
Identifiers
CAS Number	7732-18-5 Y
3D model ( JSmol )	Interactive image
Beilstein Reference	3587155
ChEBI	CHEBI:15377 Y
ChEMBL	ChEMBL1098659 Y
ChemSpider	937 Y
DrugBank	DB09145
ECHA InfoCard	100.028.902
EC Number	231-791-2
Gmelin Reference	117
KEGG	C00001
PubChem CID	962
RTECS number	ZC0110000
UNII	059QF0KO0R Y
CompTox Dashboard (EPA)	DTXSID6026296
InChI InChI=1S/H2O/h1H2 Y Key: XLYOFNOQVPJJNP-UHFFFAOYSA-N Y
SMILES O
Properties
Chemical formula	H 2O
Molar mass	18.01528(33) g/mol
Appearance	Almost colorless or white crystalline solid, almost colorless liquid, with a hint of blue, colorless gas[3]
Odor	Odorless
Density	Liquid (1 atm, VSMOW): 0.99984283(84) g/mL at 0 °C[4] 0.99997495(84) g/mL at 3.983035(670) °C (temperature of maximum density, often 4 °C)[4] 0.99704702(83) g/mL at 25 °C[4] 0.96188791(96) g/mL at 95 °C[5] Solid: 0.9167 g/mL at 0 °C[6]
Melting point	0.00 °C (32.00 °F; 273.15 K) [b]
Boiling point	99.98 °C (211.96 °F; 373.13 K)[16][b]
Solubility	Poorly soluble in methyl ethyl ketone, dichloromethane, ethyl acetate, bromine .
Vapor pressure	3.1690 kilopascals or 0.031276 atm at 25 °C[8]
Acidity (pKa)	13.995[9][10][a]
Basicity (pKb)	13.995
Conjugate acid	Hydronium H3O+ (pKa = 0)
Conjugate base	Hydroxide OH– (pKb = 0)
Thermal conductivity	0.6065 W/(m·K)[13]
Refractive index (nD)	1.3330 (20 °C)[14]
Viscosity	0.890 mPa·s (0.890 cP)[15]
Structure
Crystal structure	Hexagonal
Point group	C2v
Molecular shape	Bent
Dipole moment	1.8546 D[17]
Thermochemistry
Heat capacity (C)	75.385 ± 0.05 J/(mol·K)[16]
Std molar entropy (S⦵298)	69.95 ± 0.03 J/(mol·K)[16]
Std enthalpy of formation (ΔfH⦵298)	−285.83 ± 0.04 kJ/mol[7][16]
Gibbs free energy (ΔfG⦵)	−237.24 kJ/mol[7]
Hazards
Occupational safety and health (OHS/OSH):
Main hazards	Drowning Avalanche (as snow) Water intoxication
NFPA 704 (fire diamond)	0 0 0
Flash point	Non-flammable
Safety data sheet (SDS)	SDS
Related compounds
Other cations	Hydrogen polonide Hydrogen peroxide
Related solvents	Acetone Methanol Hydrogen fluoride Ammonia
Supplementary data page
Water (data page)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Y verify (what is YN ?) Infobox references

Water is an inorganic compound with the chemical formula H₂O. It is a transparent, tasteless, odorless,^[c] and nearly colorless chemical substance, and it is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a solvent^[19]). It is vital for all known forms of life, despite not providing food energy or organic micronutrients. Its chemical formula, H₂O, indicates that each of its molecules contains one oxygen and two hydrogen atoms, connected by covalent bonds. The hydrogen atoms are attached to the oxygen atom at an angle of 104.45°.^[20] In liquid form, H₂O is also called "Water" at standard temperature and pressure.

Because Earth's environment is relatively close to water's triple point, water exists on Earth as a solid, a liquid, and a gas.^[21] It forms precipitation in the form of rain and aerosols in the form of fog. Clouds consist of suspended droplets of water and ice, its solid state. When finely divided, crystalline ice may precipitate in the form of snow. The gaseous state of water is steam or water vapor.

Water covers about 71% of the Earth's surface, with seas and oceans making up most of the water volume (about 96.5%).

The word water comes from Old English wæter, from Proto-Germanic *watar (source also of Old Saxon watar, Old Frisian wetir, Dutch water, Old High German wazzar, German Wasser, vatn, Gothic 𐍅𐌰𐍄𐍉 (wato)), from Proto-Indo-European *wod-or, suffixed form of root *wed- ('water'; 'wet').^[27] Also cognate, through the Indo-European root, with Greek ύδωρ (ýdor; from Ancient Greek ὕδωρ (hýdōr), whence English 'hydro-'), Russian вода́ (vodá), Irish uisce, and Albanian ujë.

History

On Earth

This section is an excerpt from Origin of water on Earth § History of water on Earth.[edit]

One factor in estimating when water appeared on Earth is that water is continually being lost to space. H₂O molecules in the atmosphere are broken up by photolysis, and the resulting free hydrogen atoms can sometimes escape Earth's gravitational pull. When the Earth was younger and less massive, water would have been lost to space more easily. Lighter elements like hydrogen and helium are expected to leak from the atmosphere continually, but isotopic ratios of heavier noble gases in the modern atmosphere suggest that even the heavier elements in the early atmosphere were subject to significant losses.^[28] In particular, xenon is useful for calculations of water loss over time. Not only is it a noble gas (and therefore is not removed from the atmosphere through chemical reactions with other elements), but comparisons between the abundances of its nine stable isotopes in the modern atmosphere reveal that the Earth lost at least one ocean of water early in its history, between the Hadean and Archean eons.^{[29][clarification needed]}

Any water on Earth during the latter part of its accretion would have been disrupted by the

upper mantle and created a rock-vapor atmosphere around the young planet.^[30][31] The rock vapor would have condensed within two thousand years, leaving behind hot volatiles which probably resulted in a majority carbon dioxide atmosphere with hydrogen and water vapor. Afterward, liquid water oceans may have existed despite the surface temperature of 230 °C (446 °F) due to the increased atmospheric pressure of the CO₂ atmosphere. As the cooling continued, most CO₂ was removed from the atmosphere by subduction and dissolution in ocean water, but levels oscillated wildly as new surface and mantle cycles appeared.^[32]

Geological evidence also helps constrain the time frame for liquid water existing on Earth. A sample of pillow basalt (a type of rock formed during an underwater eruption) was recovered from the Isua Greenstone Belt and provides evidence that water existed on Earth 3.8 billion years ago.^[33] In the Nuvvuagittuq Greenstone Belt, Quebec, Canada, rocks dated at 3.8 billion years old by one study^[34] and 4.28 billion years old by another^[35] show evidence of the presence of water at these ages.^[33] If oceans existed earlier than this, any geological evidence has yet to be discovered (which may be because such potential evidence has been destroyed by geological processes like crustal recycling). More recently, in August 2020, researchers reported that sufficient water to fill the oceans may have always been on the Earth since the beginning of the planet's formation.^[36][37][38]

Unlike rocks, minerals called

cool early Earth hypothesis suggests temperatures were cold enough to freeze water between about 4.4 billion and 4.0 billion years ago. Other studies of zircons found in Australian Hadean rock point to the existence of plate tectonics as early as 4 billion years ago. If true, that implies that rather than a hot, molten surface and an atmosphere full of carbon dioxide, early Earth's surface was much as it is today (in terms of thermal insulation). The action of plate tectonics traps vast amounts of CO₂, thereby reducing greenhouse effects, leading to a much cooler surface temperature and the formation of solid rock and liquid water.^[43]

Water (

Along with oxidane, water is one of the two official names for the chemical compound H
₂O;

Water differs from most liquids in that it becomes less dense as it freezes.^[d] In 1 atm pressure, it reaches its maximum density of 999.972 kg/m³ (62.4262 lb/cu ft) at 3.98 °C (39.16 °F), or almost 1,000 kg/m³ (62.43 lb/cu ft) at almost 4 °C (39 °F).^[52][53] The density of ice is 917 kg/m³ (57.25 lb/cu ft), an expansion of 9%.^[54][55] This expansion can exert enormous pressure, bursting pipes and cracking rocks.^[56]

In a lake or ocean, water at 4 °C (39 °F) sinks to the bottom, and ice forms on the surface, floating on the liquid water. This ice insulates the water below, preventing it from freezing solid. Without this protection, most aquatic organisms residing in lakes would perish during the winter.^[57]

Magnetism

Water is a diamagnetic material.^[58] Though interaction is weak, with superconducting magnets it can attain a notable interaction.^[58]

Phase transitions

At a pressure of one

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:

$${\displaystyle {\frac {dT}{dP}}={\frac {T\left(v_{\text{L}}-v_{\text{S}}\right)}{L_{\text{f}}}}}$$

where ${\displaystyle v_{\text{L}}}$ and ${\displaystyle v_{\text{S}}}$ are the molar volumes of the liquid and solid phases, and ${\displaystyle L_{\text{f}}}$ is the molar latent heat of melting. In most substances, the volume increases when melting occurs, so the melting temperature increases with pressure. However, because ice is less dense than water, the melting temperature decreases.^[51] In glaciers, pressure melting can occur under sufficiently thick volumes of ice, resulting in subglacial lakes.^[61][62]

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.^[63] Water can remain in a liquid state at high temperatures in the deep ocean or underground. For example, temperatures exceed 205 °C (401 °F) in Old Faithful, a geyser in Yellowstone National Park.^[64] In hydrothermal vents, the temperature can exceed 400 °C (752 °F).^[65]

At

On a pressure/temperature phase diagram (see figure), there are curves separating solid from vapor, vapor from liquid, and liquid from solid. These meet at a single point called the triple point, where all three phases can coexist. The triple point is at a temperature of 273.16 K (0.01 °C; 32.02 °F) and a pressure of 611.657 pascals (0.00604 atm; 0.0887 psi);^[69] it is the lowest pressure at which liquid water can exist. Until 2019, the triple point was used to define the Kelvin temperature scale.^[70][71]

The water/vapor phase curve terminates at 647.096 K (373.946 °C; 705.103 °F) and 22.064 megapascals (3,200.1 psi; 217.75 atm).

The normal form of ice on the surface of Earth is

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 two liquid states.[53]^[80][81][82]

Taste and odor

Pure water is usually described as tasteless and odorless, although

Pure water is

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

In industry, near-infrared spectroscopy is used with aqueous solutions as the greater intensity of the lower overtones of water means that glass cuvettes with short path-length may be employed. To observe the fundamental stretching absorption spectrum of water or of an aqueous solution in the region around 3,500 cm⁻¹ (2.85 μm)^[88] a path length of about 25 μm is needed. Also, the cuvette must be both transparent around 3500 cm⁻¹ and insoluble in water; calcium fluoride is one material that is in common use for the cuvette windows with aqueous solutions.

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

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

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

Molecular polarity

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

Because of its polarity, a molecule of water in the liquid or solid state can form up to four

These bonds are the cause of water's high surface tension^[94] and capillary forces. The capillary action refers to the tendency of water to move up a narrow tube against the force of gravity. This property is relied upon by all vascular plants, such as trees.^{[citation needed]}

Self-ionization

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

Electrical conductivity and electrolysis

Pure water has a low

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).^[96]

Mechanical properties

Liquid water can be assumed to be incompressible for most purposes: its compressibility ranges from 4.4 to 5.1×10⁻¹⁰ Pa⁻¹ in ordinary conditions.^[97] Even in oceans at 4 km depth, where the pressure is 400 atm, water suffers only a 1.8% decrease in volume.^[98]

The

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

The collective mass of water found on, under, and over the surface of a planet is called the hydrosphere. Earth's approximate water volume (the total water supply of the world) is 1.386 billion cubic kilometres (333 million cubic miles).^[23]

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

Water is important in many geological processes. Groundwater is present in most

Water cycle

The water cycle (known scientifically as the hydrologic cycle) is the continuous exchange of water within the

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

Most water vapors found mostly in the ocean returns to it, but winds carry water vapor over land at the same rate as runoff into the sea, about 47 

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,^[102] 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.^[103] 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.^[104]

Seawater and tides

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

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 both photosynthesis and respiration. Photosynthetic cells use the sun's energy to split off water's hydrogen from oxygen.^[105] In the presence of sunlight, hydrogen is combined with CO
₂ (absorbed from air or water) to form glucose and release oxygen.^[106] All living cells use such fuels and oxidize the hydrogen and carbon to capture the sun's energy and reform water and CO
₂ in the process (cellular respiration).

Water is also central to acid-base neutrality and enzyme function. An acid, a hydrogen ion (H⁺
, that is, a proton) donor, can be neutralized by a base, a proton acceptor such as a hydroxide ion (OH⁻
) to form water. Water is considered to be neutral, with a

Earth's 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

Effects on human civilization

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Civilization has historically flourished around rivers and major waterways;

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.^[107][108]

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

Water reclamation is the process of converting wastewater (most commonly sewage, also called municipal wastewater) into water that can be reused for other purposes. There are 2.3 billion people who reside in nations with water scarcities, which means that each individual receives less than 1,700 cubic metres (60,000 cu ft) of water annually. 380 billion cubic metres (13×10^¹² cu ft) of municipal wastewater are produced globally each year.^{[109][110][111]}

Freshwater is a renewable resource, recirculated by the natural

In developing countries, 90% of all municipal wastewater still goes untreated into local rivers and streams.^[113] 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.^[114] 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.^[116] 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.^[117]

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.^[118] 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.^[119]

An assessment of water management in agriculture was conducted in 2007 by the

Water scarcity is also caused by production of water intensive products. For example, cotton: 1 kg of cotton—equivalent of a pair of jeans—requires 10.9 cubic meters (380 cu ft) water to produce. While cotton accounts for 2.4% of world water use, the water is consumed in regions that are already at a risk of water shortage. Significant environmental damage has been caused: for example, the diversion of water by the former Soviet Union from the Amu Darya and Syr Darya rivers to produce cotton was largely responsible for the disappearance of the Aral Sea.^[122]

• 
  Water requirement per tonne of food product
• Water distribution in subsurface drip irrigation
• 
  Irrigation of field crops

As a scientific standard

On 7 April 1795, the gram was defined in France to be equal to "the absolute weight of a volume of pure water equal to a cube of one-hundredth of a meter, and at the temperature of melting ice".^[123] For practical purposes though, a metallic reference standard was required, one thousand times more massive, the kilogram. Work was therefore commissioned to determine precisely the mass of one liter of water. In spite of the fact that the decreed definition of the gram specified water at 0 °C (32 °F)—a highly reproducible temperature—the scientists chose to redefine the standard and to perform their measurements at the temperature of highest water density, which was measured at the time as 4 °C (39 °F).^[124]

The

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

Healthy kidneys can excrete 0.8 to 1 liter of water per hour, but stress such as exercise can reduce this amount. People can drink far more water than necessary while exercising, putting them at risk of water intoxication (hyperhydration), which can be fatal.^[128][129] The popular claim that "a person should consume eight glasses of water per day" seems to have no real basis in science.^[130] Studies have shown that extra water intake, especially up to 500 milliliters (18 imp fl oz; 17 U.S. fl oz) at mealtime, was associated with weight loss.^{[131][132][133][134][135][136]} Adequate fluid intake is helpful in preventing constipation.^[137]

An original recommendation for water intake in 1945 by the Food and Nutrition Board of the

The single largest (by volume) freshwater resource suitable for drinking is Lake Baikal in Siberia.^[143]

Washing

This section is an excerpt from Washing.[edit]

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

Often people use soaps and detergents to assist in the

emulsification of oils and dirt particles so they can be washed away. The soap can be applied directly, or with the aid of a washcloth

.

People wash themselves, or bathe periodically for religious ritual or therapeutic purposes^[144] or as a recreational activity.

In

anal cleansing.^[146]

More frequent is washing of just the hands, e.g. before and after preparing food and eating, after using the toilet, after handling something dirty, etc. Hand washing is important in reducing the spread of germs.^[147][148] Also common is washing the face, which is done after waking up, or to keep oneself cool during the day. Brushing one's teeth is also essential for hygiene and is a part of washing.

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

Excessive washing may damage the hair, causing dandruff, or cause rough skin/skin lesions.^[149][150]

Transportation

Chemical uses

Water is widely used in chemical reactions as a

Heat exchange

Water and steam are a common fluid used for

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

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

Humans use water for many recreational purposes, as well as for exercising and for sports. Some of these include swimming,

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.

Municipal and

Industrial applications

Many industrial processes rely on reactions using chemicals dissolved in water, suspension of solids in water

Water is used in

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

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

Food processing

Boiling, steaming, and simmering are popular cooking methods that often require immersing food in water or its gaseous state, steam.^[154] Water is also used for dishwashing. Water also plays many critical roles within the field of food science.

Solutes in water also affect water activity that affects many chemical reactions and the growth of microbes in food.[156] Water activity can be described as a ratio of the vapor pressure of water in a solution to the vapor pressure of pure water.^[155] Solutes in water lower water activity—this is important to know because most bacterial growth ceases at low levels of water activity.^[156] Not only does microbial growth affect the safety of food, but also the preservation and shelf life of food.

According to a report published by the Water Footprint organization in 2010, a single kilogram of beef requires 15 thousand liters (3.3×10^³ imp gal; 4.0×10^³ U.S. gal) of water; however, the authors also make clear that this is a global average and circumstantial factors determine the amount of water used in beef production.[159]

Medical use

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.^[162]

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".^[163][164]

Water has been detected in interstellar clouds within the Milky Way.^[165] 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^[166]
• Atmosphere of Mercury: 3.4%, and large amounts of water in Mercury's exosphere^[167]
• Atmosphere of Venus: 0.002%^[168]
• Earth's atmosphere: ≈0.40% over full atmosphere, typically 1–4% at surface; as well as that of the Moon in trace amounts^[169]
• Atmosphere of Mars: 0.03%^[170]
• Atmosphere of Ceres^[171]
• Atmosphere of Jupiter: 0.0004%^[172] – in ices only; and that of its moon Europa^[173]
• Enceladus: 91%^[174] and Dione (exosphere)^{[citation needed}
  ]
• Atmosphere of Uranus – in trace amounts below 50 bar
• Atmosphere of Neptune – found in the deeper layers^[175]
• Extrasolar planet atmospheres: including those of HD 189733 b^[176] and HD 209458 b,^[177] Tau Boötis b,^[178] HAT-P-11b,^[179][180] XO-1b, WASP-12b, WASP-17b, and WASP-19b.^[181]
• Stellar atmospheres: not limited to cooler stars and even detected in giant hot stars such as Betelgeuse, Mu Cephei, Antares and Arcturus.^[180][182]
• IRC +10216^[185] and APM 08279+5255,^[163][164] VY Canis Majoris and S Persei.^[182]

• Mars: under the regolith and at the poles.^[192][193]
• Earth–Moon system: mainly as ice sheets on Earth and in Lunar craters and volcanic rocks^[194] 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.^[195]
• Ceres^{[196][197][198]}
• Jupiter's moons: Europa's surface and also that of Ganymede^[199] and Callisto^[200][201]
• Saturn: in the
  Enceladus^[204]
• Pluto–Charon system^[202]
• Comets^[205][206] and other related Kuiper belt and Oort cloud objects^[207]

• Mercury's poles^[208]
• Tethys^[209]

Exotic forms

Water and other

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.^[211][212]

Earth's

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^[213] and GJ 1214 b.^[214]

Law, politics, and crisis

This section needs to be updated. Please help update this article to reflect recent events or newly available information. (June 2022)

potable water

1970–2000

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

Access to safe drinking water has improved over the last decades in almost every part of the world, but approximately one billion people still lack access to safe water and over 2.5 billion lack access to adequate sanitation.^[215] However, some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability.^[216] A report, issued in November 2009, suggests that by 2030, in some developing regions of the world, water demand will exceed supply by 50%.^[217]

1.6 billion people have gained access to a safe water source since 1990.^[218] The proportion of people in developing countries with access to safe water is calculated to have improved from 30% in 1970^[219] to 71% in 1990, 79% in 2000, and 84% in 2004.^[215]

A 2006 United Nations report stated that "there is enough water for everyone", but that access to it is hampered by mismanagement and corruption.

The authors of the 2007 Comprehensive Assessment of Water Management in Agriculture cited poor governance as one reason for some forms of water scarcity. Water governance is the set of formal and informal processes through which decisions related to water management are made. Good water governance is primarily about knowing what processes work best in a particular physical and socioeconomic context. Mistakes have sometimes been made by trying to apply 'blueprints' that work in the developed world to developing world locations and contexts. The Mekong river is one example; a review by the International Water Management Institute of policies in six countries that rely on the Mekong river for water found that thorough and transparent cost-benefit analyses and environmental impact assessments were rarely undertaken. They also discovered that Cambodia's draft water law was much more complex than it needed to be.^[222]

In 2004, the UK charity WaterAid reported that a child dies every 15 seconds from easily preventable water-related diseases, which are often tied to a lack of adequate sanitation.^[223][224]

Since 2003, the

Water is considered a purifier in most religions. Faiths that incorporate ritual washing (

In Zoroastrianism, water (āb) is respected as the source of life.^[234]

Philosophy

The Ancient Greek philosopher

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

Art and activism

Painter and activist

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.[247]^[248]

Dihydrogen monoxide parody

'Dihydrogen monoxide' is a technically correct but rarely used

The word "Water" has been used by many Florida based rappers as a sort of catchphrase or adlib. Rappers who have done this include BLP Kosher and Ski Mask the Slump God.^[250] To go even further some rappers have made whole songs dedicated to the water in Florida, such as the 2023 Danny Towers song "Florida Water".^[251] Others have made whole songs dedicated to water as a whole, such as XXXTentacion, and Ski Mask the Slump God with their hit song "H2O".

See also

• Outline of water – Overview of and topical guide to water
• Water (data page) – Chemical data page for water is a collection of the chemical and physical properties of water.
• Aquaphobia – Persistent and abnormal fear of water
• Human right to water and sanitation – Human right recognized by the United Nations General Assembly in 2010
• Hydroelectricity – Electricity generated by hydropower
• Marine current power – Extraction of power from ocean currents
• Marine energy – Energy stored in the waters of oceans
• Mpemba effect – Natural phenomenon that hot water freezes faster than cold
• Oral rehydration therapy – Type of fluid replacement used to prevent and treat dehydration
• Osmotic power – Energy available from the difference in the salt concentration between seawater and river water
• Properties of water – Physical and chemical properties of pure water
• Thirst – Craving for potable fluids experienced by animals
• Tidal power – Technology to convert the energy from tides into useful forms of power
• Water pinch analysis
• Wave power – Transport of energy by wind waves, and the capture of that energy to do useful work
• Catchwater – Runoff catching or channeling device

Notes

References