Water for people.pdf - WHO Thailand Digital Repository

8 6 / A L O O K A T T H E W O R L D ’ S F R E S H W A T E R R E S O U R C E SThe Natural Water CycleTable 4.9: The world’s major water quality issuesIssue scale Water bodies polluted Sector affected Time lag between cause and effect Effects extentOrganic pollution rivers ++ aquatic environment 10 years district to regionlakes ++aquatic environmentgroundwater +Eutrophication lakes ++ aquatic environment >10 years localrivers +most usesocean fluxesSediment load rivers + aquatic environment 1–10 years regional(increase and decrease) lakes most usesocean fluxesDiversions, dams rivers ++ aquatic environment 1–10 years district to regionlakes +most usesgroundwater +++ Serious issue on a global scale++ Very serious issue on a global scalePollutants of many kinds eventually find their way into water bodies at all levels. Although it may take some years for problems to become evident, poor water quality affects both human health and ecosystemhealth.Source: WHO/UNEP, 1991.contaminated as a result of leakage from storage tanks, mine tailingsand accidental spillages (Herbert and Kovar, 1998). This contaminationhighlights the dimension of time; because groundwater systems arealmost impossible to cleanse and many contaminants are persistentand remain a hazard for long periods even at low concentrations.There are also parts of the world where naturally occurring traceelements are present in groundwater, the most prevalent being arsenicand fluoride. These cause serious health effects. Indeed, health is animportant factor in many of the world’s major water quality problemslisted by WHO/UNEP (1991) (see table 4.9).Arsenic is widely distributed throughout the earth’s crust: itoccurs in groundwater through the dissolution of minerals and ores.Long-term exposure to arsenic via drinking water causes cancer ofthe skin, lungs, urinary bladder and kidney, as well as other effects onskin such as pigmentation changes and thickening. Cancer is a lateexpression of this exposure and usually takes more than ten years todevelop. A recent study (BGS and DPHE, 2001) suggests thatBangladesh is grappling with the largest mass ‘poisoning’ in history,potentially affecting between 35 and 77 million of the country’s130 million inhabitants. Similar problems with excessiveconcentrations of arsenic in drinking water occur in a number ofother countries. Excessive amounts of fluoride in drinking water canalso be toxic. Discoloration of teeth occurs worldwide, but cripplingskeletal effects caused by long-term ingestion of large amounts areprominent in at least eight countries, including China where 30 millionpeople suffer from chronic fluorosis. The preferred remedy is to find