It has also suggested efficient management and conservation of this important natural resource as there is already a sharp decline in its per capita availability. The total demand for water by all sectors of economy, including the domestic sector will rise to 1681 bcm by 2050 which would be much in excess of present total utilisable water resources of 1086 bcm.Per capita water availability per year in terms of annual average utilisable water resources which was 3450 m3 in 1951 has declined to 1250 m3 and would be further reduced to 760 m3 by the year 2050. According to a standard estimate if the per capita water availability per year is 1000 m3, shortage will be local and rare. But the per capita water availability per year sinks below this level, water supply will begin to hamperhealth, economic development and human well being and at levels of 500 m3 per capita per year, water supply will be a primary constraint to life.

NCIWRDP has stated that need for power generation is vital for the economy and the pending power projects needed to speeded up into action in the interest of the country's economy.

The study has observed that there is a gradual shift to zero water discharge from thermal power plant. In view of this sliding scale of water use from 2.38 to 2.63 Mm3/100 MW per year in 2010, from 2.00 to 2.21 Mm3/100 MW per year in 2025 and from 1.43 to 1.58 Mm3/100 MW per year in 2050, this has been used as the norm for estimation of water requirement for energy in case of coal based thermal power stations.

Hydropower stations in general do not have any consumptive use. However, to account for unused discharges through turbines located near the sea coast, lump sum provision has been made for the stimatin. Water requirement for nuclear, wind/solar and gas based plants have beenestimated on an uniform basis.

The percentage of installed thermal, hydel and nuclear power stations are around 73, 24 and 3 of the total installed capacity, respectively.According to the Central Electricity Authority (CEA), 845 economically feasible schemes have been identified with total hydro electrical potential of 84,000 MW at 60 per cent load factor. In this context, the NCIWRDP stated that the review of sources of energy suggests that coal-based thermal power plants and in some regions, hydro power would be the mainstay of electricity generation in future. Oil, natural gas and nuclear power will account for a smaller portion.

The Fourth National Power Plan has already assumed a compound growth of 7 per cent in the installed generating capacity for the country during the period 1997-2012. Hence, the estimates of future installed capacities can also be assumed at compound rate of 7 per cent per year up to 2025 and 6 per cent during the period 2025-2050. This would, therefore, mean a sharp increase inconsumption of water.

The Indian Water Resources Society (IWRS) in its document `Water : Vision 2050' that the power sector, would require 150 bcm water by the year 2050. It has estimated that the present consumptive use of about 35 bcm by hydro power plants will rise up to about 100 bcm. In case of storage backed projects evaporation loss loss amount to 1.0 to 1.5 m in a year. This loss is estimated at about 15 per cent of the storage. Further there are westward flow of tail race water which after power generation flows to the sea as in case of Koyna, Sharavati and Supa.

In case of thermal projects, IWRS has estimated that water requirement in a 500mw coal-based plant with open cycle without reclaiming ash pond water will be 1477 m3 per hour. In case of 500mw coal based thermal unit with open cycle with reclaiming of ash pond water, water demand will be 672 m3 per hour, in case of closed cycle CT system demand for water will be 3199 m3 per hour. Thus the total consumptive water requirement for a thermalcapacity of 5 lakh mw under 3 to 5 per cent growth rate scenario would be be at least 42 bcm, assuming that 20 per cent of the capacity are located on coastal sites.The gas based and nuclear power plants would require about three bcm water. The power sector, thus would require 150 bcm water by the year 2050.