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 total annual internal renewable water resources in the region are estimated to be approximately 13,000 cubic kilometers (WRI/UNEP/UNDP, 1994). 

The per capita internal renewable water resources for Asia-Pacific countries are shown in Figure 1.10 (a-d). Per capita availability varies from about 186,000 cubic meters per year in Papua New Guinea to just over 200 cubic meters in Singapore (WRI/UNEP/UNDP/WB, 1996).(see Figures 1.10a, 1.10b, 1.10c, 1.10d) Countries such as Afghanistan and the Islamic Republic of Iran suffer from chronic water shortages due to arid climate whereas parts of the People’s Republic of China and India experience the same problem primarily due to high population density. 

Water pollution in countries in the Asia-Pacific region is caused mainly by: 

• domestic sewage,
• industrial effluents, and
• run-off from land-based activities, such as agriculture and mining.

Lake eutrophication is a significant, but localized, concern in a number of countries in South-East Asia. A survey by the United Nations Environment Programme/International Lake Environment Committee (UNEP/ILEC) showed that 54 per cent of the lakes in this sub-region were suffering from eutrophication problems (UNEP, 1994). 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. 

In the small island countries, groundwater resources are suffering from severe salinization due to the intrusion of sea water. In Thailand, the rapid lowering of the water table by excessive extraction of groundwater has caused the shallow aquifers in Bangkok to become contaminated with salt water from the nearby ocean. Over-extraction of groundwater reserves has also caused land subsidence in some cities, such as Bangkok and Jakarta. In Bangkok, for example, land has subsided by 0.5–0.6 metres in some places over the last 20–25 years; this in turn has aggravated problems of flooding in the city (ESCAP, 1995a). In countries such as Bangladesh, increased salinity and sedimentation are occuring largely as a result of upstream water withdrawal. 

The three sectors consuming the largest amount of water are agriculture, industry and domestic. The high rates of urbanization and industrialization in the region result in increasing demands for water for domestic and industrial uses. Figure 1.11(a-d) shows the variation in per capita freshwater withdrawals in the Asia-Pacific countries, ranging from 15 cubic metres to 1,400 cubic metres per capita per year (WRI/UNEP/UNDP, 1994))(see Figures 1.11a, 1.11b, 1.11c, 1.11d). Agriculture accounts for 60–90 per cent of the annual freshwater withdrawals in most of the countries of the region. The highest percentage occurs in Afghanistan where agriculture accounts for 99 per cent of the withdrawals (see Figures 1.12a, 1.12b, 1.12c, 1.12d). 

With current levels of population growth, demand for water will increase in each sector throughout the region up to and beyond the next century. Freshwater availability of less than 1,000 cubic metres of water availability per capita per year indicates water scarcity. Singapore can already be considered as short of freshwater and the Islamic Republic of Iran and India are approaching the same situation. India is also projected to be short of water before 2025. India’s water scarcity is well illustrated by the case of Rajasthan, where 8 per cent of the population use only 1 per cent of the country’s total water resources. It has also been projected that China will come close to the water stress threshold by 2025 (WRI/UNEP/UNDP, 1992). 

Different measures are being taken by many countries in the region to meet the growing demands for water and to safeguard water quality. Such measures include water reuse and recycling, seawater desalinization, demand-side management, inter-basin transfers, leak detection programmes, differential payment rates, legislation (e.g. environmental impact assessment (EIA), water and effluent standards), protection of wetlands and use of economic incentives. Many countries including Japan, Malaysia, New Zealand, the Republic of Korea and Singapore, employ economic incentives and economic instruments (such as the "polluter pays principle", tax rebates, tax write-offs, etc.) to encourage industries to reduce water pollution. 

Measures to restore water resources include river cleaning programmes, as have been undertaken by a number of countries in the region. A notable example is the 10-year "clean river" programme which was initiated by the Singapore Government in 1977. The programme, costing US$ 200 million, has brought back life to the Singapore River and the Kallang Basin. Today, the rivers support aquatic life and have dissolved oxygen (DO) concentrations ranging from 2 to 4 milligrams per litre. The Government’s objective is to reduce pollution further and to raise DO concentrations in all streams to 4 milligrams per litre by the year 2000 (Singapore Ministry of the Environment, 1992). The clean-up of the rivers was made possible through improvements in wastewater treatment and the enforcement of stringent standards (ASEAN, 1995). 

Since 1988, Hong Kong has carried out river cleaning activities which have given rise to a steady improvement in river and stream water quality. In the early 1980s, only 35 per cent of rivers were rated as fair quality or better but by 1994, 74 per cent were in these categories. Similarly, in Surabaya, Indonesia’s second largest city, a nation-wide clean river campaign programme called PROKASIH, has been instrumental in bringing greater public and political pressure onto industrial polluters. As a result, most industries have installed wastewater treatment facilities. Evidence shows that in those companies that signed voluntary PROKASIH agreements in 1991, biochemical oxygen demand (BOD) and chemical oxygen demand (COD) pollution loads fell by over 50 per cent. 

Another example of river programme is the National River Action Plan (NRAP) in India which follows a similar strategy as Phase I of the Ganga River Action Plan. The NRAP will include grossly polluted stretches of those rivers in the country which were not covered under Phases I and II of the Ganga Action Plan (GAP). The first phase of the GAP aimed to intercept, divert and treat 870 million litres of sewage per day; by December 1991, 405 million litres per day had been diverted. Phase II of the GAP would cover works required but not included in Phase I of the GAP in 25 Class I towns, and pollution abatement works in Class II and Class III towns identified on the main river Ganga. The Central Ganga Authority (CGA) identified 68 industrial units as heavy polluters and by 1992, 43 of these had installed effluent plants and 7 were in the process of doing so; 10 units were closed (Government of India 1991-92). 

A number of countries in the region have changed the emphasis in their water policies from supply to demand side management in an effort to improve water conservation. These changes include promotion of water conservation, rationalizing water prices and involving local communities through decentralized water management. Demand side management is being increasingly emphasized in order to decrease the need for heavy investments. Water conservation in Beijing has become popular in both domestic and industrial sectors and has contributed to savings of up to 30 per cent in overall consumption. Other examples of water conservation can be found in Hong Kong, where freshwater is saved by using seawater for flushing some 65 per cent of the toilets in the Territory. By 1996, Hong Kong plans to extend further the saltwater supply for flushing to 90 per cent of the population (ESCAP, 1995a).