Groundwater resources are extensive throughout the region and in some of the small island states, such as Maldives, Kiribati, Tuvalu and the Federated States of Micronesia, they form the main source of freshwater. Although the region is comparatively well endowed with water resources it has substantially below the world average per capita availability. Only about one third of the estimated renewable water resources generated by precipitation is available as run-off, another third is lost in deep percolation and the rest simply drains to the sea. The severity of water quality problems in the region is summarized in table 5. It is evident that pollution by pathogens is quite severe in South Asia, South-East Asia, the Pacific Islands and China whereas the problem is relatively minor in developed countries such as Japan, Australia and New Zealand.
Pathogens generally come from domestic sewage which is discharged into watercourses untreated.
The primary sources of organic matter pollution are domestic sewage and industrial effluents from tanneries, paper mills and textile factories. South Asia and China are the areas most severely affected by organic matter pollution, mainly from pulp, paper and food industry effluents. Lake eutrophication is a significant, but localized, concern in a number of countries in South-East Asia. The inland water bodies of the sub-region are also affected by the presence of pathogenic agents, and many rivers carry enhanced nutrient and pollutant loads resulting from changes in land use, industrialization and urbanization. The discharge of mine tailings and the development of industrial areas where pollutants are discharged directly into neighbouring river systems has resulted in localised areas of heavy metal pollution throughout the Asia-Pacific region.