ABSTRACT
Water is essential for life on earth. Water is needed for plant growth and for the survival of animals, including human beings. Of the total amount of water on earth, 97.25 per cent is contained in salty seas, 2.05 per cent is contained in glacial icecaps, and most of the remaining 0.7 per cent is contained in aquifers. The amount of renewable fresh water, available through rainfall on watershed areas for consumption by humans, is very small, approximately 0.008 per cent of the total. Of this 110,300 cubic kilometres of water, two-thirds evaporates, leaving 40,700 cubic kilometres per year of rainwater run-off, feeding rivers and replenishing aquifers and available for domestic, industrial and agricultural use. It is on this resource particularly that increasing pressure is being placed (Postel 1997; Mackenzie 1998).
