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Freshwater withdrawal from rivers, lakes, reservoirs, underground aquifers and other sources increased more in Asia during the past century than in other parts of the world, from 600 cubic kilometres in 1900 to approximately 5 000 cubic kilometres by the mid-1980s (da Cunha 1989). In Beijing, for example, the daily demand for water increased almost 100 times between 1950 and 1980 (WRI 1990). One consequence of this rapid rise in demand has been a proliferation of dams and reservoirs - between 1950 and 1986, the number of large dams increased from 1 562 to 22 389 (ICOLD 1984 and 1989).
Agriculture, mainly irrigation, accounts for the major part of water withdrawals. In the more industrialized countries, agriculture accounts for up to 50 per cent of withdrawals but this rises to more than 90 per cent in all South Asian countries except Bhutan, and reaches 99 per cent in Afghanistan (WRI, UNEP, UNDP and WB 1998).
In common with other parts of the world, the exploitation of water resources in the region has caused major disruption to hydrological cycles. Water development programmes for hydropower and to meet domestic and industrial requirements, coupled with deforestation in important watersheds, have reduced river levels and depleted wetlands. In addition, the mismanagement of water resources and increased irrigation has used groundwater reserves faster than they can be replenished, thus depleting aquifers and lowering water tables. Other activities, including the removal of vegetation from stream banks and flood control channelling, have changed the natural character of watercourses and estuaries.
Contamination by pollutants has also seriously degraded water quality, thereby reducing the amount of clean water available. The overall result has been to decrease the annual per capita availability of freshwater in the developing countries of the region from 10 000 m3 in 1950 to approximately 4 200 m3 by the early 1990s (see bar chart).
Water availability varies greatly within the region. Within Southeast Asia alone, annual per capita internal renewable water resources range from about 172 m3 a year in Singapore to more than 21 000 m3 in Malaysia (WRI, UNEP, UNDP and WB 1988). Singapore is currently meeting its freshwater demands by importing some of its supply from Malaysia. In China, water resources are estimated at 2 348 m3/capita (SEPA 1997). Supplies in India, the Islamic Republic of Iran, the Republic of Korea, Pakistan and Thailand are considerably below this, at between 1400 and 1900 a year. At the other end of the spectrum, Bhutan and Lao People's Democratic Republic have around 50 000 m3/capita and Papua New Guinea an enormous 174 000 m3/capita a year (WRI, UNEP, UNDP and WB 1998).
The region's water resources are under increasing pressure. Some arid countries, such as Afghanistan and the Islamic Republic of Iran, already have chronic water shortages. Most developing countries in the region have experienced growing water scarcity, deteriorating water quality, and sectoral conflicts over water allocation. In many parts of the region, misuse and overexploitation of water resources has resulted in the depletion of aquifers, falling water tables, shrinking inland lakes and diminished stream flows, even to ecologically-unsafe levels. Many of the Pacific islands lack adequate water storage capacity, resulting in water scarcity despite the high rainfall. This problem was highlighted by the 1997-98 'drought' in the sub-region. Drinking water supplies in coastal areas are supplemented by the coconut.
Water quality has been steadily degraded by a combination of factors including sewage and industrial effluent, urban and agricultural run-off and saline intrusion. Whilst many water quality problems are ubiquitous, others are either localized or more common in specific parts of the region.
Levels of suspended solids in Asia's rivers almost quadrupled since the late 1970s (ADB 1997, GEMS 1996) and rivers typically contain 4 times the world average and 20 times OECD levels (GEMS 1996). Sedimentation is closely tied to erosion levels and poses critical problems for most of the Mekong River, although total suspended solids (TSS) loads are not as high as in some other Asian rivers. For example, GEMS data indicate that TSS concentration in the Mekong is approximately 294 mg per litre, compared to the Ganges River at 1 130 mg per litre (MRC/UNEP 1997a). Suspended solid levels are highest in China (ADB 1997). Sediment from erosion also continues to foul rivers in Australia (Commonwealth of Australia 1996) and New Zealand, though the removal of sheep from steep pastures is now reducing sedimentation rates in some catchments in the latter (Smith and others 1993).
Water pollution caused by organic matter, pathogenic agents, and hazardous and toxic wastes is another serious problem. Biological oxygen demand (BOD) in Asian rivers is 1.4 times the world average. BOD levels declined in the early 1980s but increased in the 1990s because of increased organic waste loading. Asia's rivers contain three times as many bacteria from human waste (faecal coliform) as the world average and more than ten times OECD guidelines (ADB 1997). The reported median faecal coliform count in Asia's rivers is 50 times higher than the WHO guidelines (ADB 1997). Faecal coliform counts in Southeast Asia are the worst in the region (ADB 1997).
Asia's record with regard to safe water supply is poor. One in three Asians has no access to a safe drinking water source that operates at least part of the day within 200 metres of the home (ADB 1997). Access to safe drinking water is worst in South and Southeast Asia. Almost one in two Asians has no access to sanitation services and only 10 per cent of sewage is treated at primary level (ADB 1997). Effluent flows straight into surface or groundwater.
Dirty water and poor sanitation cause more than 500 000 infant deaths a year in the region, as well as a huge burden of illness and disability (WHO 1992). 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. For example, Asia's surface water contains 20 times more lead than surface waters in OECD countries, mainly from industrial effluents (ADB 1997). The worst lead contamination in the region is in Southeast Asia (ADB 1997). Bangladesh and some adjacent parts of India suffer from arsenic contamination of groundwater (see box). Dioxin contamination is becoming an emerging issue in Japan (NLA 1997).
Agrochemical inputs including fertilizers and pesticides, and animal wastes from livestock, are a growing source of freshwater pollution. Excessive levels of nitrates from agricultural run-off are a major cause of eutrophication throughout the region (UNESCAP/ADB 1995). Levels of nutrients, particularly phosphorus, remain unacceptably high in Australian rivers, lakes and reservoirs (Commonwealth of Australia 1996). In New Zealand, the increase in dairying and fertilizer use is intensifying pollution in shallow lakes, streams and groundwater (Smith and others 1993). 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. The region as a whole had more lakes and reservoirs with eutrophication problems (54 per cent) than Europe (53 per cent), Africa (28 per cent), North America (48 per cent) and South America (41 per cent) (UNEP 1994).
Water pollution issues vary greatly. In Southeast Asia, the industrial sector is the main source of water pollution but untreated domestic wastewater as well as chemical residues and animal wastes increasingly threaten water quality in most major rivers. In the Mekong basin, organic matter, microbes and toxic metals have polluted freshwater bodies, though most water quality problems result from natural processes (MRC/UNEP 1997a). In Japan, heavy metal and toxic chemical pollution has been reduced but surface waters are affected by organic pollution (OECD 1994). In New Zealand, the number of sewage treatment plants grew from 5 to 258 during 1950-96, reducing sewage pollution (New Zealand Ministry for the Environment 1997).
Demand for water will increase throughout the region into the next century. By 2025, India is expected to be water stressed with per capita water availability decreased to some 800 m3; China will reach the water-stress threshold before 2025 (WMO and others 1997). Southeast Asia still has adequate supplies to cope with demand over the next decade (ASEAN 1997).
While agriculture will continue to use most water, freshwater demand is growing fastest in the urban and industrial sectors. As a consequence, a major freshwater issue in many countries will be how to allocate scarce water resources among competing sectors.
Without better management practices, groundwater depletion is likely to be aggravated. At present rates of exploitation, for instance, the aquifer in Male, Maldives, is expected to be exhausted in the next few years (Government of Maldives 1994). In Mongolia, groundwater availability will be a main concern owing to the scarcity of surface water supplies.
The future quality of freshwater is one of the most pressing environmental problems in many parts of the region. Growing populations and water contamination from a wide range of sources imply reduced per capita availability in the future. The challenge will be to use dwindling supplies to satisfy a wide range of demands, and to increase national, sub-regional and regional cooperation to avoid conflict over the shared use of water resources.
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