Water is needed in almost every sphere of human activity. It is required for direct consumption or indirectly for washing, cleaning, cooling, transportation or even for waste disposal. Important sectors of human activity which require water can be grouped as follows:
1. Irrigation. 2. Thermal power generation.
3. Industries. 4. Domestic requirements.
5. Livestock management. 6. Hydro-electric generation, fisheries, navigation and recreational activities.
ADVERTISEMENTS:
According to 1970 estimates, about 3,500 cubic kms of water are drawn for human use every year. Agriculture sector is the biggest consumer of freshwater. Almost 76% of the total water used by mankind has to be diverted to grow food. To produce 20 tons of organic matter in terms of fresh weight, 2,000 tons of water has to be provided to the roots. Most of it is lost in transpiration.
Water fixed is actually 3 tons for every 5 tons of dry organic matter produced (Penman, 1970). Following agriculture, power generation (6.2%) and industries (5.7%) are the biggest consumers of fresh water. Domestic requirement and livestock management taken together consume only 4.3% of the total water drawn. Navigation, fisheries, hydro-electric power generation, recreational activities etc. also require a huge quantity of water, much of which flows down to the sea.
The amount of water drawn for human use is never used up completely. A large fraction is returned to the surface deposits or stream flows often in a polluted state which can be used again as such or after treatment to remove impurities.
Out of the total quantity of water drawn (3,500 cubic kms) the amount of water irrecoverably consumed was estimated to be about 2,200 cubic kms (L’vovich 1979). Fig. 6.2 shows the approximate percentage of the total water drawn in various sectors of human activity. The shaded area of the bars represents the portion of water which is irrecoverably used.