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Water in the 21st Century

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Water Quality, Pollution, and the Environment

Emerging Asia, published by ADB in 1997, identified water pollution as the most serious environmental problem facing the region. Water pollution exacerbates the problem of water scarcity at local and regional levels by reducing the amount of water available for productive purposes. Water pollution comes from many sources, including untreated sewage, chemical discharges, spillage of toxic materials, harmful products leached from land disposal sites, agricultural chemicals, salt from irrigation schemes, and atmospheric pollutants dissolved in rainwater. The direct disposal of domestic and industrial wastewater into watercourses is the major source of pollutants in developing countries. In Asia and the Pacific, fecal pollution is one of the most serious problems, affecting both surface water and groundwater bodies and leading to a tenacious persistence of such waterborne diseases as cholera, typhoid, and hepatitis. Estimates of the increase in water pollution loads in high growth areas of Asia over the next decades are as high as 16 times for suspended solids, 17 times for total dissolved solids, and 18 times for biological pollution loading.³ The impact of this can be seen from the following comparison: the combined volume of water used and water needed to dilute and flush pollutants is almost equal to the volume of accessible freshwater in the world's river systems.

The development of freshwater resources for human uses has compromised natural ecosystems that depend on these resources for their continued integrity. Freshwater ecosystems, comprising lakes, rivers, and wetlands, have already lost a greater proportion of species and habitat than land or ocean ecosystems. Unrestricted development of surface water and groundwater has altered the hydrologic cycle and threatens the natural functions of deltas and wetlands. Wetlands have been converted to cropland, and rivers that channeled water to estuaries and deltas have dried up. The Yellow River in the PRC, for example, is now dry during substantial portions of the year, while adjacent wetlands that tempered floods have been lost.

The Aral Sea basin illustrates vividly the extent to which human intervention has affected the natural functioning of aquatic systems. Excessive diversion of water for irrigation so reduced the flow of rivers entering the sea that its surface has shrunk by 45 percent and its volume by 70 percent since 1970. A formerly flourishing fishing industry has collapsed, and major health problems are now associated with windblown toxic salts and contaminated residues. Diminished productive potential, loss of vegetation, increased health risks, and irreversible desecration of aquatic biota are the sad legacy.

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