Water resources

WATER RESOURCES (EN: water resources; DE: Wasserschatze, Wassersquellen; FR: ressources d'eau; ES: recursos de agua; RU: водные ресурсы) are the waters, which are suitable for the usage, within the rivers, lakes, canals, reservoirs, seas and oceans, the underground waters, the soil moisture, and also the waters (ices) of the polar and mountainous glaciers, and the atmospheric precipitations.

(Table # 1) The distribution of the water resources of the Earth within the elements of the hydrosphere (according to M. I. Lvovich)
The elements of the hydrosphere The volume of the water, thousand cubic kilometres The activity of the water exchange, years
The world ocean 1 370 000 3000
The underground waters 60 000 5000*
including the zone of the active water exchange 4000* 330*
The polar glaciers 24 000 8000
The water bodies 280 7
The rivers 1.2 0.031
The soil moisture 80 1
The vapours of the atmosphere 14 0.027
The entire hydrosphere 1 458 327.2 2800
*The approximate data

During the process of the water cycle (the continuous movement of the water within the hydrosphere, atmosphere, lithosphere, in the liquid, vaporous, and solid states), there proceeds the natural renewal of the water resources (see the Table # 1). The resources of the fresh waters amount to less than 2% of the reserves of the hydrosphere. But if to exclude the polar glaciers, within which there are preserved approximately 24 million cubic kilometres of the waters (ice), which are not used, then the share of the fresh waters, which are most accessible for the usage, accounts for only 0.3% of the total volume of the hydrosphere. Nevertheless, these very waters are the most reliable source for the usage, because they are continuously renewed during the process of the water cycle. The fresh water resources, which are intensely renewed, consist of two portions, the values of which for the usage are not equal: the portion, which is more or less stable over time, and the portion, which is not stable. For example, the riverine water resources are divide d into the underground (stable) resources, which generally characterize the renewable resources of the underground waters within the zone of the active water exchange, and also the flow, which is rigidly regulated because of the flow-through lakes, and the less stable resources, namely, the superficial (of the freshet type) resources. The highly saline deep underground waters are practically non-renewable, because they do not participate within the water cycle. For the evaluation of the water resources of the mainlands, countries, river basins, and their individual parts, there has been developed the six-component system of the equations for the water balance, which permits us to evaluate various sources of the renewable water resources in the mutually associated manner, according to the water cycle, which is proper for the nature (see the Table # 2).

Theoretically, in case of the rational usage, the water resources are non-exhaustible. However, the requirements for the water resources grow so rapidly, that within many countries there is felt the acute scarcity of the water resources. The increasing of the water resources, which are accessible for the usage, is possible on the account of their extended reproduction (the usage of the agricultural and forestry activities, the creation of the water reservoirs, and other activities). Certain types of the expanded reproduction for the water resources have reached the global proportions. For example, the worldwide volume of the freshet flow, which is rigidly regulated because of the water reservoirs throughout the Earth's globe, is 2000 cubic kilometres per year, as the result of which, the natural stable drainage of the rivers within the world has increased by 16%.

The intensive economic usage of the water resources within many regions of the world leads to the significant pollution of these resources. There are formed the waste waters, which contain the residual impurities even after the purification. The quantity of such urban and industrial waste waters, which are discharged now into the rivers and water bodies of the world, reaches approximately 500 cubic kilometres per year. For the more or less complete neutralization of these waters, considering that half of them is subjected to the thorough biological purification, it is required to consume approximately 6000 cubic kilometres of the clean water per year, which amounts to approximately 17% of the total worldwide riverine flow, and in the future, under the condition of the more complete purification, it would be required to consume for this purpose the entire worldwide riverine flow.

(Table # 2) The balance estimate of the resources of the fresh waters (according to M. I. Lvovich)
The region The elements of the water balance, thousands of the cubic kilometres per year The annual provision per capita, thousand cubic metres per year
the atmospheric precipitations the riverine flow the gross moistening of the territory the evaporation
total underground superficial
Europe 7.1 3.1 1.1 2.0 5.1 4.0 4.8
Asia 32.7 13.2 3.4 9.8 22.9 19.5 5.4
Africa 20.8 4.2 1.4 2.8 18.0 16.6 9.3
North America (without the Canadian archipelago) 13.9 5.9 1.7 4.2 9.7 8.0 17.3
South America (including the Central America and West Indies) 29.3 10.3 3.7 6.6 22.7 19.0 25.6
Australia (including Oceania) 6.4 2.0 0.5 1.5 4.9 4.4 71.0
The entire dry land (without the Antarctica, Greenland, and Canadian archipelago) 110.3 38.9 12.0 26.8 83.6 71.5 9.10
USSR 10.9 4.3 1.0 3.3 7.6 6.6 16.6

The discharge of the waste waters into the rivers and water bodies, even after the purification, which may be incomplete because of the complex composition of the impurities, disrupts the desalinating action of the water cycle. For the prevention of this unfavourable phenomenon, they eliminate the industrial impurities before the discharge into the environment; they use the urban waste waters, which are containing the valuable fertilizers (nitrogen, phosphorus, potassium), after the appropriate preparation, for the fertilizing of the animal feed crops or forests, and in the certain cases, they use these waters repeatedly after the purification within those sectors of the economy, which do not require the clean water, for example, for the cooling of the turbine generators of the thermal power plants. The neutralization of the industrial waste waters specifies the transition of the purification onto the local basis, that is, the purification of the waste waters within the single pro duction line, which is containing one type of the impurities. This system, and in the certain cases, the modification of the technology of the production, permit us to transition to the closed recycling water supply. Using this method, there is achieved the isolation of the industrial segment of the water cycle from the natural segment, and the usage of the valuable wastes of the production. In the prospective future, the complete termination of the discharge of the waste waters into the rivers and water bodies is the most rational protection of the water resources.