WATER (EN: water; DE: Wasser; FR: eau; ES: agua; RU: вода) is the simplest chemical compound of hydrogen with oxygen, H2O (11.19% of hydrogen, and 88.81% of oxygen, by the mass), which is widespread within the nature, and is stable under the usual conditions; the water is the colourless liquid (of the pale bluish colour within the thick layers), without the odour, and without the taste. There belongs to the water the most important role within the geological history of the Earth, within the emergence of the life, and within the forming of the physical and chemical medium, of the climate and weather. The water is the obligatory component of practically all the technological processes.

The isotopic composition of the water. In association with the existence of the two stable isotopes of hydrogen, namely, 1H and 2H, which are usually designated as H and D (deuterium), and with the existence of the three stable isotopes of oxygen (16O, 17O, and 18O), there are known 9 isotope varieties of the water. There represents the special interest the D2O heavy water. See the Table.

The physical properties of the water, and their anomalies, are determined using the fact, that the molecules of the water are unified into the complexes using the hydrogen bonds. There exists the series of the hypothetical structural models of the water, which are requiring the further clarification.

The structure of the water is distinguished with the unstability, because the hydrogen bond is approximately by 10 times stronger, than the usual intermolecular interaction (the angle between the bonds is 104 degrees 27 minutes). The structure of the water strongly depends on the character and concentration of the admixtures, which exist as the ionic and molecular forms within the water. Various ions, and the molecules of the dissolved gases, can modify the structure of the water, for example, the atoms of helium, and the molecules of hydrogen, can be placed within the structure of the water without the disturbance of the hydrogen bonds.

The distribution of the electron density within the molecule of the water is such, that there are created the 4 poles of the charges: the 2 positive poles, which are associated with the atoms of hydrogen, and the 2 negative poles, which are associated with the electron clouds of the non-shared pairs of the electrons of the atom of oxygen. The specified poles of the charges are positioned within the vertices of the tetrahedron. Thanks to this polarity, the water has the dipole moment (1.86 D). The crystal structure of the ordinary ice is hexagonal, "loose", there are many "voids" within this structure (in case of the dense "packing" of the molecules of the water within the crystals of the ice, the density of this ice could amount to approximately 1600 kilograms per cubic metre). Within the liquid water, the bond of each H2O molecule with the four neighbour molecules (the "near order"), which is inherent to the ice, is preserved in the significant degree; however, the "lo oseness" of the structure is decreased during the melting of the ice, when the molecules of the "far order" are captured into the "voids", and this fact leads to the increase of the density of the water.

Many of the physical properties of the water reveal the substantial anomalies. The density of the water reaches the maximum value of 1000 kilograms per cubic metre at the temperature of + 3.98 degrees Celsius; during the further cooling, this density is decreased, and during the freezing, this density drops abruptly, while for almost all other substances, the crystallization is accompanied by the increase of the density. The water is capable of the significant supercooling, that is, the water may remain in the liquid state below the temperature of the melting point (even at the temperature of -30 degrees Celsius). The viscosity of the water decreases with the increasing of the pressure, but does not increase, unlike other liquids. The compressibility of the water is extremely small, and decreases with the increasing of the temperature. Certain anomalies are weakened with the increasing of the salinity of the water, and even disappear within the saturated solutions. The properties of the water may vary significantly, depending on the natural conditions, which are existing within the nature, or depending on the conditions, which are created artificially (the action of the temperature and pressure, and of the magnetic fields).

The chemical properties of the water under the usual conditions. The water is the quite stable compound, the decay of the H2O molecules becomes noticeable only at the temperature of more than 1500 degrees Celsius. The water interacts with many basic and acidic oxides, thus forming the bases and acids respectively. The joining of the water to the molecules of the unsaturated hydrocarbons lies within the basis of the industrial method for the obtainment of the alcohols, aldehydes, and ketones. The water participates within many chemical processes as the catalyst. For example, the interaction of the hydrogen or alkaline metals with the halogens, and many oxidative reactions, proceed only in the presence of at least tiny amounts of the water.

The physical parameters of the water
The density, kilograms per cubic metre
the ice 916.8 (0*C)
the liquid 999.87 (0*C)
---/--- maximal 1000.0 (3.98*C)
998.23 (20*C)
the saturated vapour 0.5977 (100*C)
The temperature of the melting point, degrees Celsius 0
The temperature of the boiling point, degrees Celsius 100
The specific heat conductivity, Watt per (metre*kelvin)
the ice 2.352 (0*C)
the liquid 0.501 (0*C)
the saturated vapour 2.314*10-2 (100*C)
The specific electric conductivity, per (Ohm * metre)
the ice 0.4*10-6 (0*C)
the liquid 1.47*10-6 (0*C)
4.41*10-6 (18*C)
1.89*10-6 (50*C)
The specific heat capacity, kilojoules per (kilogram*Kelvin)
the liquid 4.2 (15*C)
the saturated vapour 2.1 (100*C)
Dielectric permeability
the ice 74.6 (0*C)
the liquid 81.0 (20*C)
the saturated vapour 1.007 (145*C)
The viscosity, pascal*second
the liquid 1.7921*10-3 (0*C)
0.284*10-3 (100*C)
The surface tension of the liquid water at the boundary with the air, Newton per metre 0.07464 (0*C)
0.06261 (80*C)
The speed of the sound within the water, metres per second 1496 (25*C)

The gases are quite soluble within the water, if they are able to enter into the chemical interactions with this water (ammonia, hydrogen sulfide, sulfur dioxide, and carbon dioxide). Other gases are less soluble within the water. With the decreasing of the pressure, and with the increasing of the temperature (up to 80 degrees Celsius), the solubility of the gases within the water decreases. Many gases at the low temperatures, and with the increasing of the pressure, not only are dissolved within the water, but also form the crystalline hydrates.

The water is the weak electrolyte, which is dissociating according to the equation H2O ⇔ H+ + OH-, while there serves as the quantitative characteristic of the electrolytic dissociation of the water the ionic product of the water: Kw = [H+][OH-], where [H+] and [OH-] are the concentrations of the corresponding ions in terms of the gram-ions per litre; the Kw amounts to 10^-14 (at the temperature of 22 degrees Celsius) and 72 • 10^-14 (at the temperature of 100 degrees Celsius). The water dissolves the multitude of the acids, bases, and mineral salts. Such solutions conduct the electric current, thanks to the dissociation of the dissolved substances, with the forming of the hydrated ions. Many substances, in case of the dissolution within the water, enter into the reaction of the exchange decomposition with this water, and this reaction is called the hydrolysis. Among the organic substances, there may be dissolved within the water those substances, which contain the polar groups (-OH, -NH2, -COOH, and others), and have not too great molecular mass. The water itself is well soluble (or may be mixed at all ratios) only within the limited quantity of the organic solvents. However, the water exists almost always within the organic substances, at least in the form of the tiny admixture, and is able to change abruptly the physical constants of these substances. Within the nature, the water may be encountered usually in the form of the solutions.

The water within the nature. The natural water is the peculiar mineral, which is characterized by the varying chemical composition, by the existence of various admixtures, which are changing the properties of this water, and this water serves as the object for the extraction, processing, and usage in the huge quantities (approximately 3 • 10^12 cubic metres per year). Oceans, seas, lakes, water reservoirs, rivers, underground waters, and soil moisture form the water shell (see the "Hydrosphere" article). Within the atmosphere, the water is located in the form of the vapour, fog and clouds, droplets of the rain, and crystals of the snow.

Within the permafrost zone, the fresh and saltish underground gravitational waters are located in the form of the underground ice, thus causing the existence of the frozen rocks. The underground ices within the frozen rocks (especially within the dispersive rocks) change the physical properties of these rocks (abruptly increase their mechanical strength, decrease the water permeability, and so on). The saline underground waters and brines within the cryolithic zone have the negative temperatures, and undergo the changes of the composition during the fluctuations of these temperatures. There are contained within the Earth's crust, according to various estimates, from 1 to 1.3 billion cubic kilometres of the water. At the same time, the reserves of the fresh waters are rather limited. The significant quantity of the water within the Earth's crust is located within the bound state, and belongs to the structure of certain minerals and rocks (gypsum, hydrated forms of silica, hydrous silicates, and others). The constitutional water is located within the crystal lattice of the minerals in the form of the OH- ions, and much less often in the form of the H+ ions, that is, this water is formed only during the destruction of the lattice of the mineral. The crystallization water occupies the determined places within the structure of the lattice of the mineral in the form of the H2O molecules. The portion of the crystallization water, which is released without the destruction of the lattice, and which is absorbed by the mineral again during the change of the conditions, is called the zeolitic water. The molecules of the adsorption water are bound with the surface of the mineral crystals, and form the hygroscopic layer (within the minerals with the laminate structure, there are contained the interplanar layers). The adsorption water exists in the signifi cant quantities within the hard colloids. The water, which is filling the thin tubules within the soil and rock, is called the hygroscopic (capillary) water. They also distinguish the free water, which is filling the voids and cracks, and which is moving under the action of the force of gravity.

The huge quantities of the water (13-15 billion cubic kilometres) are concentrated within the mantle of the Earth. The water, which was released from the mantle during the process of the heating of the Earth at the early stages of its development, according to the modern views, has formed the hydrosphere. The annual inflow of the water from the mantle and magma chambers amounts to approximately 1 cubic kilometre (see the "Juvenile waters" article). There exist the data, that the water, at least partly, has the cosmic origin: the protons, which have come from the Sun into the upper atmosphere, after the capturing of the electrons, are transformed into the atoms of hydrogen, which, after the combining with oxygen, produce the water. All the waters of the Earth continuously interact among themselves, and also with the atmosphere, lithosphere, and biosphere. The water is the active factor of the endogenous and exogenous geologic processes, and there are tightly associated with the water the forming of the minerals, and the processes of the forming of the deposits.

Under the natural conditions, the quantitative composition of the admixtures varies, depending on the origin of the water, and on the geologic conditions. In case of the concentration of the salts of up to 1 gram per kilogram, they consider the water as fresh, up to 25 grams per kilogram as saltish, and more than this value as saline. There are the least mineralized waters the atmospheric precipitations (approximately 10-20 milligrams per kilogram on average), and then the fresh water lakes and rivers (50-1000 milligrams per kilogram). The salinity of the ocean fluctuates at approximately 35 grams per kilogram; many seas have the lesser salinity (the Black Sea has 17-22 grams per kilogram, the Baltic Sea has 8-16 grams per kilogram, the Caspian Sea has 11-13 grams per kilogram). The salinity of the underground waters near the surface under the conditions of the excessive moistening amounts up to 1 grams per kilogram, and under the arid conditions amounts up to 100 grams per kilogr am; within the deep artesian basins, the salinity of the water fluctuates within the wide limits. The maximal concentrations of the salts are observed within the salt lakes (up to 300 grams per kilogram), and within the deeply embedded underground waters (up to 600 grams per kilogram). Within the fresh waters, there usually prevail the HCO3-, Ca2+, and Mg2+ ions. The content of the Ca2+ and Mg2+ ions within the water determines the hardness of this water. With the increasing of the general salinity, there increases the concentration of the SO42-, Cl-, Na+, and K+ ions. Within the highly saline waters, there prevail the Cl- and Na+ ions, less often the Mg2+ ions, and very rarely the Ca2+ ions. Other elements are contained within the water in very small quantities, although almost all the natura l elements of the periodic system have been found within the natural waters.

The substances, which are formed during the chemical weathering of the erupted rocks (Ca2+, Mg2+, Na+, K+, and others), and which are released throughout the entire history of the Earth from its bowels (CO2, SO2, HCl, NH3, and others), are the primary sources of the salts for the natural waters. From the diversity of the composition of these substances, and of the conditions, under which there proceeded their interaction with the water, there depends the composition of this water, on the studying of which there are based the hydro-geochemical searches for the deposits of the useful minerals. The impact of the live organisms also has the great significance for the composition of the water. Of the dissolved gases, there exist within the natural waters the nitrogen, oxygen, carbon dioxide, inert gases, hydrogen sulfide, and hydrocarbons. The gas saturation of the underground waters varies from n • 10 to n • 10^3 cubic centimetres per litre. The quantity of the dissolved gas is directly proportional to the pressure of the gas, or to the partial pressure within the mixture of the gases. At the temperature of less than 100 degrees Celsius, there is observed the inverse dependence for the solubility of the gases within the water, and at the temperature of more than 100 degrees celsius, there is observed the direct dependence. The gas saturation of the water depends also on the value of the salinity, the increasing of which decreases the solubility of the gases. CO2, N2, and CH4 are the most distributed gases, which are dissolved within the underground waters. Less often, and in the smaller quantities, there are dissolved the O2, H2S, H2, heavy hydrocarbons, inert gases, and so on. There is observed the zonal distribution of the gases within the underground hydrosphere along the vertical (from the top, down): O2 N2 N2 H2S - CO2 - CH4 - N2 CH4 - N2 (or N2 - CH4) CH4 - CO2 - CH4 H2S - CO2 - CH4 (in the order of prevalence). The concentration of the organic substances is small, namely, on average, approximately 20 milligrams per litre within the rivers, and approximately 4 milligrams per litre within the oceans. The waters of the swampy and petroleum fields, and the waters, which are contaminated with the industrial and household waste waters, where the quantity of the organic substances may be greater, constitute the exception. The qualitative composition of the organic substances is extremely diverse, and includes various products of the life activity of the organisms, which are inhabiting the water, and the compounds, which are formed from their remains during the decay.

During the researches of the regularities of the forming and distribution of the natural waters, during the evaluation of the possibilities of their usage (for the drinking, household-technical, industrial, irrigation, balneology, and other purposes), during the hydro-geochemical searches for the deposits (petroleum, gas, polymetals, Br, I, B, and so on), they conduct the analysis of these waters. They determine within the waters: the physical and organoleptic properties (temperature, colour, taste, odour, turbidity, transparency, density, electrical conductivity); the content of the dissolved mineral, organic, and radioactive substances, of the free gases; various indicators (pH, Eh, hardness, oxidability, aggressiveness, and others); the isotopic and microbiological composition. The type and methods of the analysis are determined according to the purpose of the researches, and according to the required precision. During the hydro-geochemical searches for the ores, they determine the microcomponents (Cu, Pb, Sn, Ag, Mo, Be, Rb, Cs, Mn, Zn, and others); during the searches and researches for the petroleum, they determine the organic substances (acids, aromatic hydrocarbons, phenols, and others), gases, and indicator microflora; during the study of the mineral waters, they determine the specific components (As, Br, I, Fe, organic substances, and others), and gas composition (CO2, H2S, H2, O2, Rn, N2, CH4); during the searches for the water supply, and for the sanitary monitoring of the water, they determine the polluting and toxic (Pb, As, Se, Sr, and others) substances, and the bacteriologic indicators; during the evaluation of the technical properties of the water, they determine the bleaching ability, coagulation ability, corrosive properties, and filtering ability.

They analyze the water using the methods of the analytical chemistry: titrimetric and instrumental (colorimetry, photometry of the flame, photocolorimetry, spectrophotometry, potentiometry, radiometry, chromatography, and others). They perform the bacteriologic analyses using the methods of the direct counting on the membrane filters, and others. For the ensuring of the maximal preserving of the composition of the water during the analyses, there have been developed the rules for the selection, preliminary processing, and preservation of the samples (acidification, chloroformization, cooling, and others). There are limited the durations for the storage of the samples of the water before the analysis. For the analysis of the water with the small content of the components, they use the concentration, extraction, and so on.

The usage of the water. It is impossible to specify other substance, which would find so diverse and broad usage. The water is the chemical reactant, which participates within the production of the oxygen, hydrogen, alkalis, acids, alcohols, aldehydes, hydrated lime, and other substances. The water is used as the technological component for the boiling, dissolving, diluting, leaching, crystallisation, and so on. They use the water within the numerous production processes. Within the engineering, the water serves as the energy carrier (hydraulic energy industry), as the heat carrier (heating, cooling), as the working medium (steam engines). They use the natural waters for the drinking and household water supply, and for the heat supply (see the "Thermal waters" article), within the balneology (see the "Mineral waters" article), for the extraction of the valuable components from these waters (see the "Brines" article), and so on. During the performance of the mining works, they use the water for the transportation of the rocks and useful minerals within the underground mines and open-pit mines (see the "Hydraulic transport" article), for the transfer of the pressure and power during the drilling using the bottomhole motors, and also for the flushing of the boreholes, and so on. During the development of the deposits of the useful minerals, which are water flooded, there are solved comprehensively the issues of the protection of the mine workings against the water, of the lowering of the water level, of the water pumping, barrage, and drainage, of the protection of the equipment against the action of the aggressive waters, and of the usage of the water (for example, for the hydraulic destruction of the rocks, for the hydraulic stowing of the goaf space, for the dust suppression, for the siltation, for the fire prevention activities, and for the water flooding of the petroleum fields). With the usage of the water, there are conducted the beneficiation of the useful minerals, their sorting, and so on.

The changing of the properties of the water (the so-called magnetic processing) is used for the improvement of the processes of the flotation, of the water purification of the suspended substances, and so on. As the result of the industrial usage of the water, there emerges the necessity for the introduction of the water circulation systems, of the closed water cycle technologies, and of the purification of the water. In case of the discharge of the waste waters into the natural bodies of water, the purification is performed according to the norms of the maximal acceptable concentrations of the dissolved substances, and there are conducted the activities for the protection of the hydrosphere, and for the protection of the underground waters (see the "Purification of the waters" article). Within the USSR, the consumption of the water resources is regulated by the Foundations of the water legislation of the USSR and of the Union republics. There also exist the international agreements on the protection of the water resources within the frames of the CMEA, UN, and other intergovernmental organizations.