Two Russian geographers and hydrologists, Kalinin and Bykov (1969) have estimated world’s total water resources. Of 1.46 ? 109 cubic kilometers of water in the world, 93 per cent is in the oceans, 4-1 per cent is in the earth’s crust, 2.0 per cent is in glaciers and polar ice caps, and only 0 052 per cent is in fresh-water lakes, rivers, and atmospheric moisture. The annual production of freshwater by evaporation and precipitation is estimated to be 37,000 cubic kilometers. At the present time, the world’s total water use is less than 10,000 cubic kilometers, but this is estimated to increase to approximately 18,700 cubic kilometers by the year 2000.
Though there is no alarming shortage of water resource, but, there are two practical difficulties in its proper utilization-its distribution and quality. A large proportion of the world’s fresh-water falls and resides in relatively unpopulated portions of the globe, particularly Siberia and Northern Canada. Here, man’s activities are limited by other factors, and he cannot easily obtain these vast stores of water.
Secondly, the matter of water quality is of immediate concern. The principle of water reuse is now becoming accepted, so that people recognize that much of their water has been used previously by other municipal systems. Each reuse cycle, however, is increasingly become costly in terms of treatment, and each reuse cycle requires disinfectants and other industrial chemicals. Thus, water problem of the future is not going to be one of a global water shortage on a planetary basis, but one of local crisis due to concentrations of people, industry and water use, and the vagaries of weather. Certainly, the immediate concern is finding local water resources of adequate quality to meet the burgeoning needs of urban populations and intensive agriculture. The fresh-water resource can also be put under conservation and management by following methods: weather modification by cloud seeding; watershed management by manipulation and alteration of vegetation of a catchment area or watershed, in order to produce more runoff and by increasing of the storage capacity in the runoff phase so that water may be held for use in dry seasons or to prevent floods; managing water flow over land surface to get rid of any excess by drainage; controlling water supplies by storage of it by dams; controlling of floods by constructing flood control dams; channel widening, channel straightening and deepening and by construction of bypass channels; pumping out of ground water; dematerializing salt and freshwaters and lastly, melting down of glaciers and polar ice caps.