Sustainable development requires suitable supplies of clean water for drinking and cleaning. The main worldwide use of water (70-80%) is for irrigation schemes which provide water to allow crops to be grown in dry areas. A great deal of water is lost in these schemes through evaporation, and so countries which are downstream often have very little water to use, which can lead to disputes. Other uses of inland water include hydroelectric power schemes and recreational activities.
Groundwater used for freshwater drinking supplies can be easily over-exploited. When this happens it can become contaminated with salt water which makes it unsuitable for use. Water available in rivers and lakes is sometimes polluted, making it harmful to plants, animals and people. The cost of providing treatment works is usually much cheaper than the cost of dealing with disease and illness. Agenda 21 encourages investment in water treatment as a more sustainable option, especially in the developing world where up to 80% of all diseases and a third of deaths are caused by drinking contaminated water.
Proper sanitation requires a good quality water supply. A lot of pollution in water comes from human waste. The rapid growth in the populations of towns and cities in the developing world is putting pressure on governments to set up sustainable sanitation schemes to cope with large numbers of people.
The United Nations claims that the sustainable use of the worlds water resources will be achieved through co-operation between countries which share a source of water, efficient water use, and a reduction in pollution and contamination.