Water is aninorganic compound with thechemical formulaH2O. It is a transparent, tasteless, odorless,[c] andnearly colorlesschemical substance. It is the main constituent of Earth'shydrosphere and thefluids of all known living organisms, in which it acts as asolvent. Water, being apolar molecule, undergoes strong intermolecularhydrogen bonding which is a large contributor to its physical and chemical properties.[20] It is vital for all known forms of life, despite not providingfood energy or being an organicmicronutrient. Due to its presence in all organisms, its chemical stability, its worldwide abundance, and its strong polarity relative to its small molecular size, water is often referred to as the "universal solvent".[21]
Because Earth's environment is relatively close to water'striple point, water exists on Earth as a solid, a liquid, and a gas.[22] It formsprecipitation in the form of rain andaerosols in the form offog. Clouds consist of suspended droplets of water andice, its solid state. When finely divided,crystalline ice may precipitate in the form of snow. The gaseous state of water issteam orwater vapor.
Water plays an important role in theworld economy. Approximately 70% of thefresh water used by humansgoes to agriculture.[26] Fishing insalt andfresh 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.[27] Much of the long-distance trade of commodities (such as oil, natural gas, and manufactured products) istransported 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,snowboarding, andskiing.
Etymology
The wordwater comes fromOld Englishwæter, fromProto-Germanic*watar (source also ofOld Saxonwatar,Old Frisianwetir,Dutchwater,Old High Germanwazzar, GermanWasser,vatn,Gothic𐍅𐌰𐍄𐍉 (wato)), fromProto-Indo-European*wod-or, suffixed form of root*wed- ('water';'wet').[28] Alsocognate, through the Indo-European root, with Greekύδωρ (ýdor; from Ancient Greekὕδωρ (hýdōr), whence English'hydro-'), Russianвода́ (vodá), Irishuisce, andAlbanianujë.
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 byphotolysis, and the resulting freehydrogen atoms can sometimesescape Earth's gravitational pull. When the Earth was younger and lessmassive, water would have been lost to space more easily.[29] Lighter elements like hydrogen andhelium are expected to leak from the atmosphere continually, butisotopic ratios of heaviernoble gases in the modern atmosphere suggest that even the heavier elements in the early atmosphere were subject to significant losses.[30] 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, a volume of water approximately equal to modern ocean volume, early in its history. This is likely to have occurred between theHadean andArchean eons in cataclysmic events such as the moon forming impact.[31]
Any water on Earth during the latter part of its accretion would have been disrupted by theMoon-forming impact (~4.5 billion years ago), which likely vaporized much of Earth's crust andupper mantle and created a rock-vapor atmosphere around the young planet.[32][33] The rock vapor would have condensed within two thousand years, leaving behind hot volatiles which probably resulted in a majoritycarbon dioxide atmosphere with hydrogen andwater 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.[34] As the cooling continued, most CO2 was removed from the atmosphere bysubduction and dissolution in ocean water, but levels oscillated wildly as new surface andmantle cycles appeared.[35]
This pillow basalt on the seafloor near Hawaii was formed when magma extruded underwater. Other, much older pillow basalt formations provide evidence for large bodies of water long ago in Earth's history.
Geological evidence also helps constrain the time frame for liquid water existing on Earth. A sample ofpillow basalt (a type of rock formed during an underwater eruption) was recovered from theIsua Greenstone Belt and provides evidence that water existed on Earth 3.8 billion years ago.[36] In theNuvvuagittuq Greenstone Belt, Quebec, Canada, rocks dated at 3.8 billion years old by one study[37] and 4.28 billion years old by another[38] show evidence of the presence of water at these ages.[36] 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 likecrustal recycling). More recently, in August 2020, researchers reported that sufficient water to fill the oceans may have always been on theEarth since the beginning of theplanet's formation.[39][40][41]
Unlike rocks, minerals calledzircons are highly resistant to weathering and geological processes and so are used to understand conditions on the very early Earth. Mineralogical evidence from zircons has shown that liquid water and an atmosphere must have existed 4.404 ± 0.008 billion years ago, very soon after the formation of Earth.[42][43][44][45] This presents somewhat of a paradox, as thecool early Earth hypothesis suggests temperatures were cold enough to freeze water between about 4.4 billion and 4.0 billion years ago.[46] Other studies of zircons found in Australian Hadean rock point to the existence ofplate tectonics as early as 4 billion years ago.[47] 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 ofthermal insulation). The action of plate tectonics traps vast amounts of CO2, thereby reducinggreenhouse effects, leading to a much cooler surface temperature and the formation of solid rock and liquid water.[48]
A water molecule consists of two hydrogen atoms and one oxygen atom.
Water (H2O) is apolarinorganic compound. Atroom temperature it is atasteless andodorless liquid, nearlycolorless with ahint of blue. The simplesthydrogen chalcogenide, it is by far the most studied chemical compound and is sometimes described as the "universal solvent" for its ability to dissolve more substances than any other liquid,[49][50] though it is poor at dissolving nonpolar substances.[51] This allows it to be the "solvent of life":[52] indeed, water as found in nature almost always includes various dissolved substances, and special steps are required to obtain chemicallypure water. Water is the only common substance to exist as a solid, liquid, and gas in normal terrestrial conditions.[53]
Water is one of only a few common naturally occurring substances which, for some temperature ranges, become lessdense as they cool, and the only known naturally occurring substance which does so while liquid. In addition it is unusual as it becomes significantly lessdense as it freezes, though it is not unique in that respect.[d]
Ways of presenting the density of water using five metric units of length, volume, and mass.
At 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).[58][59]
Below that temperature, but above the freezing point of 0 °C (32 °F), it expands becoming less dense until it reaches freezing point, reaching a density in its liquid phase of 999.8 kg/m3 (62.4155 lb/cu ft).
Once it freezes and becomes ice, it expands by about 9%, with a density of 917 kg/m3 (57.25 lb/cu ft).[60][61] This expansion can exert enormous pressure, bursting pipes and cracking rocks.[62] As a solid, it displays the usual behavior of contracting and becoming more dense as it cools. These unusual thermal properties have important consequences for life on earth.
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.[63] In addition, this anomalous behavior is an important part of thethermohaline circulation which distributes heat around the planet's oceans.
Magnetism
Water is adiamagnetic material.[64] Though interaction is weak, with superconducting magnets it can attain a notable interaction.[64]
Phase transitions
At a pressure of oneatmosphere (atm), ice melts or water freezes (solidifies) at 0 °C (32 °F) and water boils or vapor condenses at 100 °C (212 °F). However, even below the boiling point, water can change to vapor at its surface byevaporation (vaporization throughout the liquid is known asboiling). Sublimation and deposition also occur on surfaces.[56] For example,frost is deposited on cold surfaces whilesnowflakes form by deposition on an aerosol particle or ice nucleus.[65] In the process offreeze-drying, a food is frozen and then stored at low pressure so the ice on its surface sublimates.[66]
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 theClausius–Clapeyron relation:
where and are themolar volumes of the liquid and solid phases, and is the molarlatent 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.[57] In glaciers,pressure melting can occur under sufficiently thick volumes of ice, resulting insubglacial lakes.[67][68]
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.[69] Water can remain in a liquid state at high temperatures in the deep ocean or underground. For example, temperatures exceed 205 °C (401 °F) inOld Faithful, a geyser inYellowstone National Park.[70] Inhydrothermal vents, the temperature can exceed 400 °C (752 °F).[71]
At sea level, the boiling point of water is 100 °C (212 °F). As atmospheric pressure decreases with altitude, the boiling point decreases by 1 °C every 274 meters.High-altitude cooking takes longer than sea-level cooking. For example, at 1,524 metres (5,000 ft), cooking time must be increased by a fourth to achieve the desired result.[72] Conversely, apressure cooker can be used to decrease cooking times by raising the boiling temperature.[73] In a vacuum, water will boil at room temperature.[74]
Triple and critical points
Phase diagram of water
On a pressure/temperaturephase diagram (see figure), there are curves separating solid from vapor, vapor from liquid, and liquid from solid. These meet at a single point called thetriple 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);[75] it is the lowest pressure at which liquid water can exist.Until 2019, the triple point was used to define theKelvin temperature scale.[76][77]
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).[78] This is known as thecritical point. At higher temperatures and pressures the liquid and vapor phases form a continuous phase called asupercritical 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 canmix freely withnonpolar compounds, including mostorganic compounds. This makes it useful in a variety of applications including high-temperatureelectrochemistry and as an ecologically benign solvent orcatalyst in chemical reactions involving organic compounds. In Earth's mantle, it acts as a solvent during mineral formation, dissolution and deposition.[79][80]
The normal form of ice on the surface of Earth isice Ih, a phase that forms crystals withhexagonal symmetry. Another withcubic crystalline symmetry,ice Ic, can occur in the upper atmosphere.[81] As the pressure increases, ice forms othercrystal structures. As of 2024, twenty have been experimentally confirmed and several more are predicted theoretically.[82] The eighteenth 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.[83][84] When sandwiched between layers ofgraphene, ice forms a square lattice.[85]
The details of the chemical nature of liquid water are not well understood; some theories suggest that its unusual behavior is due to the existence of two liquid states.[59][86][87][88]
Taste and odor
Pure water is usually described as tasteless and odorless, although humans have specific sensors that can feel the presence of water in their mouths,[89][90] and frogs are known to be able to smell it.[91] However, water from ordinary sources (includingmineral 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 thepotability of water to avoid water that is too salty orputrid.[92]
Pure water isvisibly blue due toabsorption of light in the region c. 600–800 nm.[93] 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 areovertones of the O–H stretchingvibrations. The apparent intensity of the color increases with the depth of the water column, followingBeer'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 glasscuvettes 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)[94] 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.
TheRaman-active fundamental vibrations may be observed with, for example, a 1 cm sample cell.
Aquatic plants,algae, and otherphotosynthetic organisms can live in water up to hundreds of meters deep, becausesunlight can reach them.Practically no sunlight reaches the parts of the oceans below 1,000 metres (3,300 ft) of depth.
Therefractive index of liquid water (1.333 at 20 °C (68 °F)) is much higher than that of air (1.0), similar to those ofalkanes andethanol, but lower than those ofglycerol (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
Tetrahedral structure of water
In a water molecule, the hydrogen atoms form a 104.5° angle with the oxygen atom. The hydrogen atoms are close to two corners of a tetrahedron centered on the oxygen. At the other two corners arelone 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.[95][96] The O–H bond length is about 0.096 nm.[97]
Other substances have a tetrahedral molecular structure, for examplemethane (CH 4) andhydrogen sulfide (H 2S). However, oxygen is moreelectronegative than most other elements, so the oxygen atom has a negative partial charge while the hydrogen atoms are partially positively charged. Along with the bent structure, this gives the molecule anelectrical dipole moment and it is classified as apolar molecule.[98]
Because of its polarity, a molecule of water in the liquid or solid state can form up to fourhydrogen bonds with neighboring molecules. Hydrogen bonds are about ten times as strong as theVan 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 ofother analogous compounds like hydrogen sulfide. They also explain its exceptionally highspecific heat capacity (about 4.2J/(g·K)),heat of fusion (about 333 J/g),heat of vaporization (2257 J/g), andthermal conductivity (between 0.561 and 0.679 W/(m·K)). These properties make water more effective at moderating Earth'sclimate, 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.[99]
These bonds are the cause of water's highsurface tension[100] and capillary forces.Capillary action refers to the tendency of water to move up a narrow tube against the force ofgravity. This property is relied upon by allvascular plants, such as trees.[101]
Water is a weak solution of hydronium hydroxide—there is an equilibrium2H 2O ⇌H 3O+ +OH− , in combination with solvation of the resultinghydronium andhydroxide ions.
Liquid water can be split into theelements hydrogen and oxygen by passing an electric current through it—a process calledelectrolysis. The decomposition requires more energy input than theheat released by the inverse process (285.8 kJ/mol, or 15.9 MJ/kg).[103]
Mechanical properties
Liquid water can be assumed to be incompressible for most purposes: its compressibility ranges from 4.4 to5.1×10−10 Pa−1 in ordinary conditions.[104] Even in oceans at 4 km depth, where the pressure is 400 atm, water suffers only a 1.8% decrease in volume.[105]
Theviscosity of water is about 10−3 Pa·s or 0.01poise at 20 °C (68 °F), and thespeed of sound in liquid water ranges between 1,400 and 1,540 metres per second (4,600 and 5,100 ft/s) depending on temperature. Sound travels long distances in water with littleattenuation, especially at low frequencies (roughly 0.03dB/km for 1 kHz), a property that is exploited bycetaceans and humans for communication and environment sensing (sonar).[106]
Hydrology is the study of the movement, distribution, and quality of water throughout the Earth. The study of the distribution of water ishydrography. The study of the distribution and movement ofgroundwater ishydrogeology, of glaciers isglaciology, of inland waters islimnology and distribution of oceans isoceanography. Ecological processes with hydrology are in the focus ofecohydrology.
The collective mass of water found on, under, and over the surface of a planet is called thehydrosphere. Earth's approximate water volume (the total water supply of the world) is 1.386 billion cubic kilometres (333 million cubic miles).[24]
Liquid water is found inbodies of water, such as an ocean, sea, lake, river, stream,canal, pond, orpuddle. The majority of water on Earth isseawater. Water is also present in the atmosphere in solid, liquid, and vapor states. It also exists as groundwater inaquifers.
Water is important in many geological processes. Groundwater is present in mostrocks, and the pressure of this groundwater affects patterns offaulting. Water in themantle is responsible for the melt that producesvolcanoes atsubduction zones. On the surface of the Earth, water is important in both chemical and physicalweathering processes. Water, and to a lesser but still significant extent, ice, are also responsible for a large amount ofsediment transport that occurs on the surface of the earth.Deposition of transported sediment forms many types ofsedimentary rocks, which make up thegeologic record ofEarth history.
The water cycle (known scientifically as the hydrologic cycle) is the continuous exchange of water within thehydrosphere, between theatmosphere,soil water,surface water, groundwater, and plants.
Water moves perpetually through each of these regions in thewater cycle consisting of the following transfer processes:
evaporation from oceans and other water bodies into the air andtranspiration from land plants and animals into the air.
precipitation, from water vapor condensing from the air and falling to the earth or ocean.
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 while 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, andhail, with some contribution fromfog anddew.[110] 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.[111] Condensed water in the air may alsorefractsunlight to producerainbows.
Water runoff often collects overwatersheds flowing into rivers. Througherosion, runoff shapes the environment creating rivervalleys anddeltas 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 oflatitude.
Water resources arenatural resources of water that are potentially useful for humans,[112] for example as a source of drinkingwater supply orirrigation 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.[113] 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, causinggroundwater depletion.[114]
Seawater contains about 3.5%sodium chloride on average, plus smaller amounts of other substances. The physical properties of seawater differ fromfresh 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 theBaltic Sea to 4.0% in theRed Sea. (TheDead Sea, known for its ultra-high salinity levels of between 30 and 40%, is really asalt lake.)
Tides are the cyclic rising and falling of local sea levels caused by thetidal forces of the Moon and the Sun acting on the oceans. Tides cause changes in the depth of the marine andestuarine 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 theeffects of Earth rotation and the localbathymetry. The strip of seashore that is submerged at high tide and exposed at low tide, theintertidal zone, is an important ecological product of ocean tides.
From abiological standpoint, water has many distinct properties that are critical for the proliferation of life. It carries out this role by allowingorganic compounds to react in ways that ultimately allowreplication. All known forms of life depend on water. Water is vital both as asolvent in which many of the body's solutes dissolve and as an essential part of manymetabolic processes within the body. Metabolism is the sum total ofanabolism andcatabolism. In anabolism, water is removed from molecules (through energy requiring enzymatic chemical reactions) to grow larger molecules (e.g., starches, triglycerides, and proteins for storage of fuels and information). In catabolism, water is used to break bonds 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.[115] In the presence of sunlight, hydrogen is combined withCO 2 (absorbed from air or water) to form glucose and release oxygen.[116] All living cells use such fuels and oxidize the hydrogen and carbon to capture the sun's energy and reform water andCO 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 apH (the negative log of the hydrogen ion concentration) of 7 in an ideal state.Acids have pH values less than 7 whilebases have values greater than 7.
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 asamphibians, spend portions of their lives in water and portions on land. Plants such askelp andalgae grow in the water and are the basis for some underwater ecosystems.Plankton is generally the foundation of the oceanfood chain.
Aquatic vertebrates must obtain oxygen to survive, and they do so in various ways. Fish havegills instead oflungs, although some species of fish, such as thelungfish, have both.Marine mammals, such as dolphins, whales,otters, andseals 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 (seeinsect andmollusc siphons) andgills (Carcinus). However, as invertebrate life evolved in an aquatic habitat most have little or no specialization for respiration in water.
An environmental science program – a student fromIowa State University sampling water
Water fit for human consumption is calleddrinking water or potable water. Water that is not potable may be made potable by filtration ordistillation, or by a range ofother methods. More than 660 million people do not have access to safe drinking water.[117][118]
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 calledsafe 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 aschlorine orozone or by the use ofultraviolet light.
Water reclamation is the process of converting wastewater (most commonlysewage, also called municipal wastewater) into water that can bereused 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.[119][120][121]
Freshwater is a renewable resource, recirculated by the naturalhydrologic 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 theMillennium Development Goals for water to halve by 2015 the proportion of people worldwide without access to safe water andsanitation. Progress toward that goal was uneven, and in 2015 the UN committed to theSustainable Development Goals of achieving universal access to safe and affordable water and sanitation by 2030. Poorwater quality and bad sanitation are deadly; some five million deaths a year are caused by water-related diseases. TheWorld Health Organization estimates thatsafe water could prevent 1.4 million child deaths fromdiarrhea each year.[122]
In developing countries, 90% of allmunicipal wastewater still goes untreated into local rivers and streams.[123] Some 50 countries, with roughly a third of the world's population, also suffer from medium or highwater scarcity and 17 of these extract more water annually than is recharged through their natural water cycles.[124] The strain not only affects surface freshwater bodies like rivers and lakes, but it also degrades groundwater resources.
Total water withdrawals for agricultural, industrial and municipal purposes per capita, measured in cubic metres (m3) per year in 2010[125]
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.[126] 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.[127]
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 ofpeak water.[128] 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.[129]
An assessment of water management in agriculture was conducted in 2007 by theInternational Water Management Institute in Sri Lanka to see if the world had sufficient water to provide food for its growing population.[130] 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 ofphysical water scarcity, where there is not enough water to meet all demands. A further 1.6 billion people live in areas experiencingeconomic 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.[131]
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 metres (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 formerSoviet Union from theAmu Darya andSyr Darya rivers to produce cotton was largely responsible for the disappearance of theAral Sea.[132]
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".[133] 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 reproducibletemperature—the scientists chose to redefine the standard and to perform their measurements at the temperature of highest waterdensity, which was measured at the time as 4 °C (39 °F).[134]
TheKelvin temperature scale of theSI system was based on thetriple point of water, defined as exactly 273.16 K (0.01 °C; 32.02 °F), but as of May 2019 is based on theBoltzmann constant instead. The scale is anabsolute temperature scale with the same increment as the Celsius temperature scale, which was originally defined according to theboiling point (set to 100 °C (212 °F)) andmelting point (set to 0 °C (32 °F)) of water.
Natural water consists mainly of the isotopes hydrogen-1 and oxygen-16, but there is also a small quantity of heavier isotopes oxygen-18, oxygen-17, and hydrogen-2 (deuterium). The percentage of the heavier isotopes is very small, but it still affects the properties of water. Water from rivers and lakes tends to contain less heavy isotopes than seawater. Therefore, standard water is defined in theVienna Standard Mean Ocean Water specification.
A young girl drinkingbottled waterWater availability: the fraction of the population using improved water sources by countryRoadside fresh water outlet from glacier,Nubra
Thehuman body contains, on average, 50–60% water, depending on age, gender and body size, although individuals may have anywhere between 45% and 75%.[135] TheU.S. National Academies of Sciences, Engineering, and Medicine recommends a daily intake of 3.7 liters (0.98 U.S. gallons) of water for adult men and 2.7 L (0.71 U.S. gal) for women.[136] 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.[137] 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.[138]
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 ofwater intoxication (hyperhydration), which can be fatal.[139][140] The popular claim that "a person should consume eight glasses of water per day" seems to have no real basis in science.[141] Studies have shown that extra water intake, especially up to 500 millilitres (18 imp fl oz; 17 US fl oz) at mealtime, was associated with weight loss.[142][143] Adequate fluid intake is helpful in preventing constipation.[144]
An original recommendation for water intake in 1945 by the Food and Nutrition Board of theU.S. National Research Council read: "An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods."[145] The latest dietary reference intake report by the U.S. National Research Council in general recommended, based on the median total water intake from US survey data (including food sources): 3.7 litres (0.81 imp gal; 0.98 US gal) for men and 2.7 litres (0.59 imp gal; 0.71 US gal) of water total for women, noting that water contained in food provided approximately 19% of total water intake in the survey.[146]
Specifically, pregnant and breastfeeding women need additional fluids to stay hydrated. The USInstitute of Medicine recommends that, on average, men consume 3 litres (0.66 imp gal; 0.79 US gal) and women 2.2 litres (0.48 imp gal; 0.58 US gal); pregnant women should increase intake to 2.4 litres (0.53 imp gal; 0.63 US gal) and breastfeeding women should get 3 liters (12 cups), since an especially large amount of fluid is lost during nursing.[136] Also noted is that normally, about 20% of water intake comes from food, while the rest comes from drinking water and beverages (caffeinated included). Water is excreted from the body in multiple forms; throughurine andfeces, throughsweating, 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.
Often people use soaps and detergents to assist in theemulsification of oils and dirt particles so they can be washed away. The soap can be applied directly, or with the aid of awashcloth or assisted withsponges or similarcleaning tools.
In social contexts, washing refers to the act ofbathing, or washing different parts of the body, such ashands,hair, orfaces. Excessive washing may damage the hair, causing dandruff, or cause rough skin/skin lesions.[155][156] Some washing of the body is done ritually in religions like Christianity and Judaism, as anact of purification.
Washing can also refer to washing objects. For example,washing of clothing or other cloth items, like bedsheets, orwashing dishes or cookwear. Keeping objects clean, especially if they interact with food or the skin, can help with sanitation. Other kinds of washing focus on maintaining cleanliness and durability of objects that get dirty, suchwashing one's car, by lathering the exterior with car soap, or washing tools used in a dirty process.
Maritime transport (or ocean transport) or more generally waterborne transport, is the transport of people (passengers) or goods (cargo) viawaterways.Freight transport bywatercraft has been widely used throughout recorded history, as it provides a higher-capacity mode of transportation for passengers and cargo than land transport, the latter typically being more costly per unitpayload due to it being affected byterrain conditions and road/rail infrastructures. The advent of aviation during the 20th century has diminished the importance of sea travel for passengers, though it is still popular forshort trips andpleasure cruises. Transport by watercraft is much cheaper than transport by aircraft or land vehicles (both road and rail),[157] but is significantly slower for longer journeys and heavily dependent on adequate port facilities. Maritime transport accounts for roughly 80% of international trade, according toUNCTAD in 2020.
Maritime transport can be realized over any distance as long as there are connectingbodies of water that are navigable to boats, ships orbarges such as oceans, lakes, rivers and canals. Shipping may be for commerce,recreation, or military purposes, and is an important aspect of logistics in human societies since early shipbuilding andriver engineering were developed, leading tocanal ages in various civilizations. While extensive inland shipping is less critical today, the major waterways of the world including many canals are still very important and are integral parts of worldwide economies. Particularly, especially any material can be moved by water; however, water transport becomes impractical when material delivery is time-critical such as various types of perishableproduce. Still, water transport is highly cost effective with regular schedulable cargoes, such as trans-oceanic shipping of consumer products – and especially for heavy loads orbulk cargos, such as coal,coke,ores or grains. Arguably, theIndustrial Revolution had its first impacts where cheap water transport by canal, navigations, orshipping by all types of watercraft on natural waterways supported cost-effectivebulk transport.
Containerization revolutionized maritime transport starting in the 1970s. "General cargo" includes goods packaged in boxes, cases, pallets, and barrels. When a cargo is carried in more than one mode, it isintermodal orco-modal.
Chemical uses
Water is widely used in chemical reactions as asolvent orreactant and less commonly as asolute or catalyst. In inorganic reactions, water is a common solvent, dissolving many ionic compounds, as well as other polar compounds such asammonia andcompounds 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 isamphoteric (acidicand basic) andnucleophilic. Nevertheless, these properties are sometimes desirable. Also, acceleration ofDiels-Alder reactions by water has been observed.Supercritical water has recently been a topic of research. Oxygen-saturated supercritical water combusts organic pollutants efficiently.
Heat exchange
Water and steam are a common fluid used forheat exchange, due to its availability and highheat capacity, both for cooling and heating. Cool water may even be naturally available from a lake or the sea. It is especially effective to transport heat throughvaporization andcondensation of water because of its largelatent heat of vaporization. A disadvantage is that metals commonly found in industries such as steel and copper areoxidized faster by untreated water and steam. In almost allthermal 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 byevaporation in acooling tower). In the United States, cooling power plants is the largest use of water.[158]
In thenuclear power industry, water can also be used as aneutron moderator. In mostnuclear reactors, water is both a coolant and a moderator. This provides something of a passive safety measure, as removing the water from the reactor alsoslows 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.
Water has a high heat of vaporization and is relatively inert, which makes it a goodfire 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 asteam 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, orcoke graphite, decompose the water, producingwater gas.
The power of such explosions was seen in theChernobyl 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 hotzirconium.
Some metallic oxides, most notably those ofalkali metals andalkaline earth metals, produce so much heat in reaction with water that a fire hazard can develop. The alkaline earth oxidequicklime, also known as calcium oxide, 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.[159]
Humans use water for many recreational purposes, as well as for exercising and for sports. Some of these include swimming,waterskiing,boating,surfing anddiving. In addition, some sports, likeice hockey andice skating, are played on ice. Lakesides, beaches andwater 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 insideaquariums or ponds for show, fun, and companionship. Humans also use water for snow sports, such asskiing,sledding,snowmobiling orsnowboarding, which require the water to be at a low temperature either as ice or crystallized into snow.
Drinking water is often collected atsprings, extracted from artificialborings (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 harmfulmicrobes. Popular methods arefiltering with sand which only removes undissolved material, whilechlorination andboiling kill harmful microbes.Distillation does all three functions. More advanced techniques exist, such asreverse osmosis.Desalination of abundantseawater is a more expensive solution used in coastalaridclimates.
The distribution of drinking water is done throughmunicipal water systems, tanker delivery or asbottled 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 toconserve 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 asexternalities 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 onaquatic life if theybioaccumulate and if they are notbiodegradable.
Many industrial processes rely on reactions using chemicals dissolved in water, suspension of solids in waterslurries or using water to dissolve and extract substances, or to wash products or process equipment. Processes such as mining,chemical pulping,pulp bleaching,paper manufacturing, textile production, dyeing, printing, and cooling of power plants use large amounts of water, requiring a dedicated water source, and often cause significant water pollution.
Water is used inpower generation.Hydroelectricity is electricity obtained fromhydropower. 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 inwater blasting andwater 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 thesteam turbine andheat exchanger, in addition to its use as a chemicalsolvent. Discharge of untreated water from industrial uses ispollution. Pollution includes discharged solutes (chemical pollution) and discharged coolant water (thermal pollution). Industry requires pure water for many applications and uses a variety of purification techniques both in water supply and discharge.
Food processing
Water can be used to cook foods such asnoodles.Sterile water for injection
Boiling,steaming, andsimmering are popular cooking methods that often require immersing food in water or its gaseous state, steam.[160] Water is also used fordishwashing. Water also plays many critical roles within the field offood science.
Solutes such as salts and sugars found in water affect the physical properties of water. The boiling and freezing points of water are affected by solutes, as well asair pressure, which is in turn affected by altitude. Water boils at lower temperatures with the lower air pressure that occurs at higher elevations. Onemole of sucrose (sugar) per kilogram of water raises the boiling point of water by 0.51 °C (0.918 °F), and one mole of salt per kg raises the boiling point by 1.02 °C (1.836 °F); similarly, increasing the number of dissolved particles lowers water's freezing point.[161]
Solutes in water also affect water activity that affects many chemical reactions and the growth of microbes in food.[162] Water activity can be described as a ratio of the vapor pressure of water in a solution to the vapor pressure of pure water.[161] Solutes in water lower water activity—this is important to know because most bacterial growth ceases at low levels of water activity.[162] Not only does microbial growth affect the safety of food, but also the preservation and shelf life of food.
Water hardness is also a critical factor in food processing and may be altered or treated by using a chemical ion exchange system. It can dramatically affect the quality of a product, as well as playing a role in sanitation. Water hardness is classified based on concentration of calcium carbonate the water contains. Water is classified as soft if it contains less than 100 mg/L (UK)[163] or less than 60 mg/L (US).[164]
According to a report published by the Water Footprint organization in 2010, a single kilogram of beef requires 15 thousand litres (3.3×10^3 imp gal; 4.0×10^3 US 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.[165]
Band 5ALMA receiver is an instrument specifically designed to detect water in the universe.[167]
Much of the universe's water is produced as a byproduct ofstar 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.[168]
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 aquasar 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".[169][170]
Water has been detected ininterstellar clouds within theMilky Way.[171] 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 theformation and evolution of the Solar System and that of other star systems, most otherplanetary systems are likely to have similar ingredients.
Liquid water is present on Earth, covering 71% of its surface.[23] Liquid water is also occasionally present in small amountson Mars.[193] Scientists believe liquid water is present in the Saturnian moons ofEnceladus, as a 10-kilometre thick ocean approximately 30–40 kilometers below Enceladus' south polar surface,[194][195] andTitan, as a subsurface layer, possibly mixed withammonia.[196] Jupiter's moonEuropa has surface characteristics which suggest a subsurface liquid water ocean.[197] Liquid water may also exist on Jupiter's moonGanymede as a layer sandwiched between high pressure ice and rock.[198]
Water ice
Water is present as ice on:
Water ice in theKorolev crater on MarsMars: under the regolith and at the poles.[199][200]
Earth–Moon system: mainly asice sheets on Earth and in Lunar craters and volcanic rocks[201] 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.[202]
Water and othervolatiles probably comprise much of the internal structures ofUranus andNeptune and the water in the deeper layers may be in the form ofionic water in which the molecules break down into a soup of hydrogen and oxygen ions, and deeper still assuperionic water in which the oxygen crystallizes, but the hydrogen ions float about freely within the oxygen lattice.[217]
The existence of liquid water, and to a lesser extent its gaseous and solid forms, on Earth are vital to the existence oflife on Earth as we know it. The Earth is located in thehabitable zone of theSolar System; if it were slightly closer to or farther from theSun (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.[218][219] Earth's size also plays a role: itsgravity allows it to hold anatmosphere, includingair moisture. Smaller planets like Mars have extremely thin or no atmospheres.[220] Water vapor and carbon dioxide in the atmosphere provide a temperature buffer (greenhouse effect) which helps maintain a relatively steady surface temperature.[citation needed]
The surface temperature of Earth has been relatively constant throughgeologic 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 atmosphericalbedo. This proposal is known as theGaia hypothesis.[citation needed]
The state of water on a planet depends on ambient pressure, which is determined by the planet's gravity. If a planet is sufficiently massive, the water on it may be solid even at high temperatures, because of the high pressure caused by gravity, as it was observed on exoplanetsGliese 436 b[221] andGJ 1214 b.[222]
This section needs to beupdated. Please help update this article to reflect recent events or newly available information.(June 2022)
An estimate of the proportion of people in developing countries with access topotable water 1970–2000
Water politics is politics affected by water andwater 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 adequatesanitation.[223] However, some observers have estimated that by 2025 more than half of theworld population will be facing water-based vulnerability.[224] A report, issued in November 2009, suggests that by 2030, in some developing regions of the world, water demand will exceed supply by 50%.[225]
1.6 billion people have gained access to a safe water source since 1990.[226] The proportion of people indeveloping countries withaccess to safe water is calculated to have improved from 30% in 1970[227] to 71% in 1990, 79% in 2000, and 84% in 2004.[223]
A 2006 United Nations report stated that "there is enough water for everyone", but that access to it is hampered by mismanagement and corruption.[228] In addition, global initiatives to improve the efficiency of aid delivery, such as theParis 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.[229]
The authors of the 2007Comprehensive 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 theInternational 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.[230]
In 2004, the UK charityWaterAid reported that a child dies every 15 seconds from easily preventable water-related diseases, which are often tied to a lack of adequate sanitation.[231][232]
Since 2003, theUN World Water Development Report, produced by theUNESCOWorld Water Assessment Programme, has provided decision-makers with tools for developing sustainablewater policies.[233] The 2023 report states that two billion people (26% of the population) do not have access todrinking water and 3.6 billion (46%) lack access to safely managed sanitation.[234] People in urban areas (2.4 billion) will facewater scarcity by 2050.[233] Water scarcity has been described as endemic, due tooverconsumption and pollution.[235] The report states that 10% of the world's population lives in countries with high or critical water stress. Yet over the past 40 years, water consumption has increased by around 1% per year, and is expected to grow at the same rate until 2050. Since 2000, flooding in the tropics has quadrupled, while flooding in northern mid-latitudes has increased by a factor of 2.5.[236] The cost of these floods between 2000 and 2019 was 100,000 deaths and $650 million.[233]
People come to Inda Abba Hadera spring (Inda Sillasie, Ethiopia) to wash in holy water.
Water is considered a purifier in most religions. Faiths that incorporate ritual washing (ablution) include Christianity,[239]Hinduism,Islam, Judaism, theRastafari movement,Shinto,Taoism, andWicca. Immersion (oraspersion oraffusion) of a person in water is a centralSacrament of Christianity (where it is calledbaptism); it is also a part of the practice of other religions, including Islam (Ghusl), Judaism (mikvah) andSikhism (Amrit Sanskar). In addition, a ritual bath in pure water is performed for the dead in many religions including Islam and Judaism. In Islam, the five daily prayers can be done in most cases after washing certain parts of the body using clean water (wudu), unless water is unavailable (seeTayammum). In Shinto, water is used in almost all rituals to cleanse a person or an area (e.g., in the ritual ofmisogi).
In Christianity,holy water is water that has been sanctified by a priest for the purpose ofbaptism, theblessing of persons, places, and objects, or as a means of repelling evil.[240][241]
The Ancient Greek philosopherEmpedocles sawwater as one of the fourclassical elements (along with fire, earth, andair), and regarded it as anylem, 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, amonist, believed further that all things are made from water.Plato believed that the shape of water is anicosahedron – flowing easily compared to the cube-shaped earth.[243]
Some traditional and popularAsian philosophical systems take water as a role-model.James Legge's 1891 translation of theDao 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) theTao" 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."[244]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.[245]
In the significantmodernist novelUlysses (1922) by Irish writerJames Joyce, the chapter "Ithaca" takes the form of acatechism of 309 questions and answers, one of which is known as the "water hymn".[246]: 91 According to Richard E. Madtes, the hymn is not merely a "monotonous string of facts", rather, its phrases, like their subject, "ebb and flow, heave and swell, gather and break, until they subside into the calm quiescence of the concluding 'pestilential fens, faded flowerwater, stagnant pools in the waning moon.'"[246]: 79 The hymn is considered one of the most remarkable passages in Ithaca, and according to literary criticHugh Kenner, achieves "the improbable feat of raising to poetry all the clutter of footling information that has accumulated in schoolbooks."[246]: 91 Theliterary motif of water represents the novel's theme of "everlasting, everchanging life," and the hymn represents the culmination of the motif in the novel.[246]: 91 The following is the hymn quoted in full.[247]
What in water did Bloom, waterlover, drawer of water, watercarrier returning to the range, admire? Its universality: its democratic equality and constancy to its nature in seeking its own level: its vastness in the ocean of Mercator’s projection: its unplumbed profundity in the Sundam trench of the Pacific exceeding 8,000 fathoms: the restlessness of its waves and surface particles visiting in turn all points of its seaboard: the independence of its units: the variability of states of sea: its hydrostatic quiescence in calm: its hydrokinetic turgidity in neap and spring tides: its subsidence after devastation: its sterility in the circumpolar icecaps, arctic and antarctic: its climatic and commercial significance: its preponderance of 3 to 1 over the dry land of the globe: its indisputable hegemony extending in square leagues over all the region below the subequatorial tropic of Capricorn: the multisecular stability of its primeval basin: its luteofulvous bed: its capacity to dissolve and hold in solution all soluble substances including millions of tons of the most precious metals: its slow erosions of peninsulas and downwardtending promontories: its alluvial deposits: its weight and volume and density: its imperturbability in lagoons and highland tarns: its gradation of colours in the torrid and temperate and frigid zones: its vehicular ramifications in continental lakecontained streams and confluent oceanflowing rivers with their tributaries and transoceanic currents: gulfstream, north and south equatorial courses: its violence in seaquakes, waterspouts, artesian wells, eruptions, torrents, eddies, freshets, spates, groundswells, watersheds, waterpartings, geysers, cataracts, whirlpools, maelstroms, inundations, deluges, cloudbursts: its vast circumterrestrial ahorizontal curve: its secrecy in springs, and latent humidity, revealed by rhabdomantic or hygrometric instruments and exemplified by the well by the hole in the wall at Ashtown gate, saturation of air, distillation of dew: the simplicity of its composition, two constituent parts of hydrogen with one constituent part of oxygen: its healing virtues: its buoyancy in the waters of the Dead Sea: its persevering penetrativeness in runnels, gullies, inadequate dams, leaks on shipboard: its properties for cleansing, quenching thirst and fire, nourishing vegetation: its infallibility as paradigm and paragon: its metamorphoses as vapour, mist, cloud, rain, sleet, snow, hail: its strength in rigid hydrants: its variety of forms in loughs and bays and gulfs and bights and guts and lagoons and atolls and archipelagos and sounds and fjords and minches and tidal estuaries and arms of sea: its solidity in glaciers, icebergs, icefloes: its docility in working hydraulic millwheels, turbines, dynamos, electric power stations, bleachworks, tanneries, scutchmills: its utility in canals, rivers, if navigable, floating and graving docks: its potentiality derivable from harnessed tides or watercourses falling from level to level: its submarine fauna and flora (anacoustic, photophobe) numerically, if not literally, the inhabitants of the globe: its ubiquity as constituting 90% of the human body: the noxiousness of its effluvia in lacustrine marshes, pestilential fens, faded flowerwater, stagnant pools in the waning moon.
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.[257][258]
'Dihydrogen monoxide' is a technically correct but rarely usedchemical name of water. This name has been used in a series ofhoaxes andpranks that mockscientific illiteracy. This began in 1983, when anApril Fools' Day article appeared in a newspaper inDurand, Michigan. The false story consisted of safety concerns about the substance.[259]
Music
The word "Water" has been used by many Florida basedrappers as a sort of catchphrase or adlib. Rappers who have done this includeBLP Kosher andSki Mask the Slump God.[260] To go even further some rappers have made whole songs dedicated to the water in Florida, such as the 2023Danny Towers song "Florida Water".[261] Others have made whole songs dedicated to water as a whole, such asXXXTentacion, and Ski Mask the Slump God with their hit song "H2O".
^A commonly quoted value of 15.7 used mainly in organic chemistry for the pKa of water is incorrect.[12][13]
^abVienna Standard Mean Ocean Water (VSMOW), used for calibration, melts at 273.150089(10) K (0.000089(10) °C, and boils at 373.1339 K (99.9839 °C). Other isotopic compositions melt or boil at slightly different temperatures.
^"naming molecular compounds".www.iun.edu. Archived fromthe original on 24 September 2018. Retrieved1 October 2018.Sometimes these compounds have generic or common names (e.g., H2O is "water") and they also have systematic names (e.g., H2O, dihydrogen monoxide).
^abcTanaka M, Girard G, Davis R, Peuto A, Bignell N (August 2001). "Recommended table for the density of water between 0 C and 40 C based on recent experimental reports".Metrologia.38 (4):301–309.Bibcode:2001Metro..38..301T.doi:10.1088/0026-1394/38/4/3.
^Ramires ML, Castro CA, Nagasaka Y, Nagashima A, Assael MJ, Wakeham WA (1 May 1995). "Standard Reference Data for the Thermal Conductivity of Water".Journal of Physical and Chemical Reference Data.24 (3):1377–1381.Bibcode:1995JPCRD..24.1377R.doi:10.1063/1.555963.ISSN0047-2689.
^Lide 2003, 8—Concentrative Properties of Aqueous Solutions: Density, Refractive Index, Freezing Point Depression, and Viscosity.
^abcdWater in Linstrom, Peter J.; Mallard, William G. (eds.);NIST Chemistry WebBook, NIST Standard Reference Database Number 69, National Institute of Standards and Technology, Gaithersburg (MD)
^PubChem."Water". National Center for Biotechnology Information.Archived from the original on 3 August 2018. Retrieved25 March 2020.
^abBelnay L."The water cycle"(PDF).Critical thinking activities. Earth System Research Laboratory.Archived(PDF) from the original on 20 September 2020. Retrieved25 March 2020.
^Fellows P (2017). "Freeze drying and freeze concentration".Food processing technology: principles and practice (4th ed.). Kent: Woodhead Publishing/Elsevier Science. pp. 929–940.ISBN978-0-08-100523-1.OCLC960758611.
^Siegert MJ, Ellis-Evans JC, Tranter M, Mayer C, Petit JR, Salamatin A, et al. (December 2001). "Physical, chemical and biological processes in Lake Vostok and other Antarctic subglacial lakes".Nature.414 (6864):603–609.Bibcode:2001Natur.414..603S.doi:10.1038/414603a.PMID11740551.S2CID4423510.
^Wagner W, Pruß A (June 2002). "The IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use".Journal of Physical and Chemical Reference Data.31 (2): 398.doi:10.1063/1.1461829.
^Adschiri T, Lee YW, Goto M, Takami S (2011). "Green materials synthesis with supercritical water".Green Chemistry.13 (6): 1380.doi:10.1039/c1gc15158d.
^Nakamoto K (1997).Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part A: Theory and Applications in Inorganic Chemistry (5th ed.). New York: Wiley. p. 170.ISBN0-471-16394-5.
^Isaacs ED, Shukla A, Platzman PM, Hamann DR, Barbiellini B, Tulk CA (1 March 2000). "Compton scattering evidence for covalency of the hydrogen bond in ice".Journal of Physics and Chemistry of Solids.61 (3):403–406.Bibcode:2000JPCS...61..403I.doi:10.1016/S0022-3697(99)00325-X.
^Fine RA, Millero FJ (1973). "Compressibility of water as a function of temperature and pressure".Journal of Chemical Physics.59 (10): 5529.Bibcode:1973JChPh..59.5529F.doi:10.1063/1.1679903.
^Halka M, Nordstrom B (2010).Alkali and Alkaline Earth Metals: Alkali and Alkaline-Earth Metals. Periodic Table of the Elements. New York: Infobase Learning. p. 8.ISBN978-0-8160-7369-6.
^Ropp RC (2013).Encyclopedia of the alkaline earth compounds. Oxford: Elsevier. p. 2.ISBN978-0-444-59553-9.
^UNEP International Environment (2002).Environmentally Sound Technology for Wastewater and Stormwater Management: An International Source Book. IWA.ISBN978-1-84339-008-4.OCLC49204666.
^Food and Nutrition Board, National Academy of Sciences. Recommended Dietary Allowances. National Research Council, Reprint and Circular Series, No. 122. 1945. pp. 3–18.
^"Microbial fact sheets",Guidelines for drinking-water quality: Fourth edition incorporating the first and second addenda, World Health Organization, 2022, retrieved1 September 2025
^Sridharan R, Ahmed S, Dasa TP, Sreelathaa P, Pradeepkumara P, Naika N, et al. (2010). "'Direct' evidence for water (H2O) in the sunlit lunar ambience from CHACE on MIP of Chandrayaan I".Planetary and Space Science.58 (6): 947.Bibcode:2010P&SS...58..947S.doi:10.1016/j.pss.2010.02.013.
^"JPL".NASA Jet Propulsion Laboratory (JPL). Archived fromthe original on 4 June 2012.
^Lloyd, Robin."Water Vapor, Possible Comets, Found Orbiting Star", 11 July 2001,Space.com. Retrieved 15 December 2006.Archived 23 May 2009 at theWayback Machine
^Ehlers, E., Krafft, T, eds. (2001). "J.C.I. Dooge. "Integrated Management of Water Resources"".Understanding the Earth System: compartments, processes, and interactions. Springer. p. 116.
^"Habitable Zone".The Encyclopedia of Astrobiology, Astronomy and Spaceflight.Archived from the original on 23 May 2007. Retrieved26 April 2007.
^"World Water Day".United Nations.Archived from the original on 9 September 2020. Retrieved10 September 2020.
^"About".World Oceans Day Online Portal.Archived from the original on 20 September 2020. Retrieved10 September 2020.
^Z Wahrman M (2016).The Hand Book: Surviving in a Germ-Filled World. University Press of New England. pp. 46–48.ISBN978-1-61168-955-6.Water plays a role in other Christian rituals as well. ... In the early days of Christianity, two to three centuries after Christ, the lavabo (Latin for "I wash myself"), a ritual handwashing vessel and bowl, was introduced as part of Church service.
^Chambers's encyclopædia, Lippincott & Co (1870). p. 394.
^Altman, Nathaniel (2002)Sacred water: the spiritual source of life. pp. 130–133.ISBN1-58768-013-0.
^Lindberg, D. (2008).The beginnings of western science: The European scientific tradition in a philosophical, religious, and institutional context, prehistory to A.D. 1450 (2nd ed.). Chicago: University of Chicago Press.
^Tao Te Ching.Archived from the original on 12 July 2010. Retrieved25 July 2010 – via Internet Sacred Text Archive Home.
UNESCO World Water Assessment Programme (2025). The United Nations World Water Development Report 2025, Mountains and glaciers: water towers (Report).doi:10.54679/LHPJ5153.ISBN978-92-3-100743-9.
.svg)
.jpeg)
