Introduction to water and waste – global parameters Water resources

Water is the most important of all natural resources for both land conservation and the welfare of mankind. The basic need to support life is 4 litres of water daily and an average city dweller requires about 400 litres per day for his needs and services; washing, cleaning, cooking and bathing.

The total volume of water present in the world has been estimated by UNESCO at 1,454 million cu km. 97% of this water is contained in saline oceans and 69% of what remains is in the form of snow and ice. Freshwater for human use, found in lakes, swamps and rivers makes up only 0.008% of the earth’s water. The world’s natural store of freshwater is found in high altitudes, in the glaciers of Greenland, Antarctica, North America and Russia. Freshwater is an essential component of life on earth and disruption of the cycle of water supply and demand can have catastrophic effects upon land, vegetation, animals and humans. Too little water leads to parched landscapes, crop destruction, reduced numbers of wildlife and in extreme cases famine among humans. Too much water can ruin land and crops, kill wildlife and devastate human settlements. Because the water cycle renews the flow of rivers, groundwater and glaciers, actual run off from these sources can exceed 47,000 cubic km per year.

Water is stored in aquifers, which are large subterranean caverns. In parts of the Middle East and North Africa the ratio of groundwater use to aquifer recharge is currently estimated at 4:1. Up to 3,000 tones of water is needed to produce one tonne of wheat in these and other arid regions.

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