Water pollution

Posted: 26 March 2008

Not only is freshwater water being over-used and wasted, it is also increasingly polluted. Each year roughly 450 cubic kilometres of waste water are discharged into rivers, streams and lakes. To dilute and transport this dirty water before it can be used again, another 6,000 cubic kilometres of clean water are needed - an amount equal to about two-thirds of the world's total annual useable freshwater runoff. If current trends were to continue, the world's entire stable river flow would be needed just for pollutant transport and dilution by the middle of this century.

In developing countries, on average, 90 per cent of all domestic sewage and 75 per cent of all industrial wastes are discharged into surface waters with minimal treatment or none at all.

Polluted water, Sao Paulo, Brazil. Credit: UN-Habitat

Consider the following examples:

  • Over three quarters of China's 50,000 kilometres of major rivers are so filled with pollution and sediment that they no longer support fish life.

  • In greater Sao Paulo, Brazil, 300 metric tons of untreated effluents from 1,200 industries flow untreated into the Tiete River every day. The river contains high concentrations of lead, cadmium and other heavy metals.

  • In Thailand and Malaysia water pollution is so heavy that rivers often contain 30 to 100 times more pathogens, heavy metals and poisons from industry and agriculture than is permitted by government health standards.

  • All of India's 14 major rivers are badly polluted. Together they transport 50 million cubic metres of untreated sewage into India's coastal waters every year.

  • Developed countries have polluted their surface waters as well. Two thirds of Europe's major rivers contain excessive loads of oxygen-robbing nitrogen and phosphorus from chemical fertilizers, along with pesticide residues, industrial effluents and municipal wastes.

  • Take the Mississippi River. America's largest river - which drains 40 per cent of the lower 48 States - transports more than 1.6 million metric tons of nitrogen every year into the Gulf of Mexico. Most of the nitrogen comes from agricultural activities. The nitrogen and other pollutants carried by river have created a "dead zone" that extends some 60 miles offshore. Expanding every year, it now encompasses an area the size of Rhode Island.