[5] A number of classifications exist for denoting the amounts of ground water. In the major part of them there is a difference between resources and reserves. Notion "resources'' was introduced to hydrogeology by Academician F. P. Savarensky.
[6] He based the necessity of introduction of this notion for ground waters by the fact that ground waters do not have permanent reserves as other mineral resources because they are permanently renewed in the process of general water cycle. In the use of ground waters it is frequently needed to take into account not only the volume occupied by ground waters in the given basin or water layer but to know the inflow of ground waters. Therefore, F. P. Savarensky considered that it would be more correct to speak not about the reserves of ground waters but about their resource understanding this term as their supply (feeding) and consumption, while term "reserves'' is related only for the amount of waters, which is located in the given basin (or water bearing layer) not depending on its capacity. The capacity of water bearing layer and the reserves of ground water in this layer cannot be large, but the productivity of this layer can be high if it is provided with supply. On the contrary, a basin of ground waters can possess large size but annual supply of water into the layer can appear small.
[7] Let us mention one important peculiarity of ground waters related to the estimate of perspectives of their use. This is the fact that the possibility of pumping of ground waters depends not only on the amount of water contained in the layer and supplied to the layer in the natural conditions but also on the filtration properties of water bearing rocks determining the resistance to the spreading of ground waters to the water intake structures.
[8] According to the data of the European Commission on Economy, ground waters are the main source of the urban economical and drinking water supply in the majority of European countries. Water supply of such large European cities (with the population of approximately one million people and greater) as Budapest, Vienna, Hamburg, Copenhagen, Munich, Rome are completely or almost completely based on ground waters, while in such cities as Amsterdam, Brussels, and Lisbon ground water cover more than a half of the total water consumption.
[9] At the same time, the use of ground waters as the source of full-scale centralized water supply has a number of strong restrictions. In many cases, daily provision of large and largest cities with ground waters at the amounts of hundreds of thousand and even millions of cubic meters is not a real goal owing to the limited resources of ground waters in relation to the necessity of creating a system of hundreds or even thousands of water intake wells on a large territory, whose construction and operation requires enormous assignments.
[10] There is another very important aspect, which should be always kept in mind in the solution of the problem of ground water use. They are tightly related to the other components of the environment. Any variations, for example, in the amount of the atmospheric precipitation inevitably cause variations in the regime, resources, and quality of ground waters. On the contrary, variations in the ground waters lead to variations in the environment. Intense pumping of ground waters by concentrated water intake systems can lead to inadmissible decrease in the surface sink, subsidence of the earth's surface, depression of vegetation related to ground waters, and activation of karst processes. Intake of ground waters can entrain mineralized waters from deep water bearing levels, which are not applicable for drinking, while in the coastal regions the inflow can include saline sea waters. All these facts should be taken into account in the planning of ground water use.
[11] Estimate of natural and operation resources of ground waters is the practice of hydrogeological studies. Natural resources (dynamic reserves) characterize the amount of ground water supply due to infiltration of atmospheric precipitation, absorption of rivers discharge and overflow from other water bearing layers, which form a total amount of the discharge of the flow and thickness of water layer transported to the level of ground waters. Thus, natural resources are indicators of ground water renewal reflecting their main peculiarity as a replenished mineral.
[12] A strict water legislation exists in Russia (as well as it was in the USSR) and in a number of other countries. According to this legislation, fresh ground waters of high quality should be first of all used for economical and drinking water supply. Only in those regions, where estimated resources of ground waters are sufficient for satisfying the existing and perspective requirements in water of drinking quality it is possible to use fresh ground water for other purposes (including irrigation) not related to drinking water supply of the population with the permission of nature protection bodies. It is our opinion that such legislation is principally correct. We should use surface waters to the requirements not related to drinking water supply. It can be sometimes more expensive than the use of ground waters, but we should do this first of all to conserve fresh ground waters for our children and grandchildren.
[13] The plans of ground water use should take into account the fact that protection of different water bearing layers from pollution is not the same.
[14] Pressure water layers overlaid by poorly penetrable clayey layers are practically completely protected from the penetration of contaminants from the surface. In this case, pollution can be related only with unsatisfactory technical state of intake and prospecting wells. Spring waters in foothill and mountainous regions are reliably protected from pollution in the cases when no industrial activity is held in the regions of their supply. Ground waters of first water bearing layers from the surface are much worse protected especially in river valleys where ground waters are tightly related to surface waters, and inflow of surface polluted waters occurs during intake of ground waters. However, even in these cases, protection of ground waters is much greater than river waters because self-purification occurs during the propagation of polluted waters in the column of rocks. However, in all cases where it is possible reliably protected waters from deep pressure levels and spring waters are more preferable.
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