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FACTS ABOUT WATER QUALITY The quality of natural water in rivers, lakes and reservoirs and below the ground surface depends on a number of interrelated factors. These factors include geology, climate, topography, biological processes and land use. The most frequent sources of pollution are human waste (with 2 million tons a day disposed of in watercourses), industrial waste and chemicals, and agricultural pesticides and fertilizers. Key forms of pollution include faecal coliforms, industrial organic substances, acidifying substances from mining aquifers and atmospheric emissions, heavy metals from industry, ammonia, nitrate and phosphate pollution and pesticide residues from agriculture, sediments from human-induced erosion to rivers, lakes and reservoirs. Shiklomanov (2004) provides estimates of the volume of wastewater produced by each continent, which gave a global total in excess of 1,500 km3 for 1995. Then there is the contention that each litre of wastewater pollutes at least 8 litres of freshwater, so based on this figure some 12,000 km3 of the globe’s water resources are not available for use. If this figure keeps pace with population growth, then with an anticipated population of 9 billion by 2050, the world’s water resources would be reduced by some 18,000 km3. Levels of suspended solids in rivers in Asia have risen by a factor of four over the last three decades. Asian rivers also have a biological oxygen demand some 1.4 times the global average, as well as three times as many bacteria from human waste as the global average. A recent study (BGS and DPHE, 2001) suggests that Bangladesh is grappling with the largest mass ‘poisoning’ (concentrations of arsenic in drinking water) in history, potentially affecting between 35 and 77 million of the country’s 130 million inhabitants. Excessive amounts of fluoride in drinking water can also be toxic. Discoloration of teeth occurs worldwide, but crippling skeletal effects caused by long-term ingestion of large amounts are prominent in at least eight countries, including China, where 30 million people suffer from chronic fluorosis.
Information from: Source: UNESCO Water Portal, May 2005
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