The cause of arsenic contamination in groundwater has not yet been established with certainty but natural geological changes are presumed to be the primary cause. MoHFW 1998 Water pollution caused by organic matter, pathogenic agents, and hazardous and toxic wastes is another serious problem. BOD levels declined in the early 1980s but increased in the 1990s because of increased organic waste loading. Asia's record with regard to safe water supply is poor. Access to safe drinking water is worst in South and Southeast Asia.
Effluent flows straight into surface or groundwater.
According to WHO, diarrhoea associated with contaminated water poses the most serious threat to health in the region and the region accounted for about 40 per cent of the total global diarrhoea episodes in the under-fives during 1990. A number of toxic pollutants also affect human health. Agrochemical inputs including fertilizers and pesticides, and animal wastes from livestock, are a growing source of freshwater pollution. During the 1990s, freshwater resources in the Mekong basin suffered moderate to severe eutrophication. Eutrophication of surface water is also becoming a serious problem in Southeast Asia.