One of most ancient ways of protection from water, its regulation and use was a way of delay of water current by construction of dams and creation of reservoirs. The man for thousand and hundreds years has done huge work on creation of artificial reservoirs and construction of dams.

In this table only the items of information about rather large reservoirs are given. However, not less than 20 thousand reservoirs with volume more than 10 mln m³ exist. There is also huge number of small reservoirs, volumed in tens thousand and thousands of cubic meters. So only in USA almost 1,9 mln of reservoirs of volume less than 60 thousand m ³ is totaled. Volume of small reservoirs makes size equal to about quarter of volume of large reservoirs, therefore total volume of all reservoirs of the world makes approximately 7500 km³.The work, done by the man, on regulation of a drain of the rivers by reservoirs is a huge achievement, as it has helped to solve a number of the important tasks: to irrigate about 240 mln hectare of ground, which gives half of agricultural production of the world, occupying 1/6th part of used grounds; to receive a plenty of the electric power - manufacturing of hydroelectric power stations makes 1736 mlrd kVt?h (the year 1980), or 20,1 % from general manufacture of the electric power; to protect the large populated territories from floods. At last, the great benefit of reservoirs is that they increase volume of a guaranteed steady river drain, as the delay of a revolution of water due to them is comparable to delay of a revolution of water in an active zone of underground waters. In other words, the reservoirs as though increase an underground component of a river drain and this increase makes now about 7500 km ³ per year, or 50 % from a world underground drain of the rivers.