The World’s total water resources are estimated at 1.36 × 108 ? ha-m. Of these global water resources, about 97.2% is salt water mainly in oceans, and only 2.8% is available as fresh water at any time on the planet earth. Out of this 2.8% of fresh water, about 2.2% is available as surface water and 0.6% as ground water. Even out of this 2.2% of surface water, 2.15% is fresh water in glaciers and icecaps and only of the order of 0.01% is available in lakes and
streams, the remaining 0.04% being in other forms. Out of 0.6% of stored ground water, only about 0.25% can be economically extracted with the present drilling technology (the remaining being at greater depths). It can be said that the ground water potential of the Ganga Basin is roughly about forty times the flow of water in the river Ganga. The rivers of north India are perennial (i.e., the water in sufficient quantity flows in them throughout the year) since they receive the snow melt runoff in summer. Rivers of peninsular India (south India) receive only runoff due to rainfall and have a good flow only during monsoons; many of them are either dry or have negligible flow during most of the remaining part of the year.