According to the UN estimates, the total amount of water on earth is about 1400 million cubic kilometer (m.cu.km.) which is enough to cover the earth with a layer of 3000 meters depth. However the fresh water constitutes a very small proportion of this enormous quantity. About 2.7 per cent of the total water available on the earth is fresh water of which about 75.2 per cent lies frozen in polar regions and another 22.6 per cent is present as ground water. The rest is available in lakes, rivers, atmosphere, moisture, soil and vegetation. What is effectively available for consumption and other uses is a small proportion of the quantity available in rivers, lakes and ground water. The crisis about water resources development and management thus arises because most of the water is not available for use and secondly it is characterised by its highly uneven spatial distribution. Accordingly, the importance of water has been recognised and greater emphasis is being laid on its economic use and better management.