Effects of modifying water environments on water supply and human health

Due to increasing population and per-capita water demand, demands for water are increasing in many parts of the world. Consequently, overuse of limited water resources leaves only small amounts of water in rivers and is bringing about rapid drawdown of groundwater tables. Water resources are affected by human activities such as excessive inputs of nutrients and other contaminants, agriculture and aquaculture expansions, and many development activities. The combined effects of modifying the water environments, both in terms of quantity and quality, on water supply and human health are presented in the paper with some examples from the Asian countries. In rural and sub-urban areas in Bangladesh and Vietnam, for example, the traditional way of obtaining surface water from ponds had been replaced by taking groundwaters to avert the microbial health risks that had arisen from contamination by human wastes. Such a change of water sources, however, has brought about human health impact caused by arsenic on a massive scale. In Thailand, the industrial development has driven the residents to get groundwater leaden with very high fluoride. Monitoring the urine fluoride levels reveal the risk of drinking fluoride-laden groundwaters. Rivers are also affected by extensive exploitation such as sand mining. As a result, turbidity changes abruptly after a heavy rainfall. In cities, due to shrinking water resources they have to take poor quality waters from contaminated sources. Algal blooms are seen in many reservoirs and lakes due to increasing levels of nutrients. Hence, it is likely that algal toxins may enter the water supply systems. Because most of the water treatment plants are not designed to remove those known and unknown contaminants, it is estimated that quite a large number of people are now under the threat of the public health "gtime bomb,"h which may one day bring about mass-scale health problems. In order to mitigate the negative impacts of modifying the water environments on human health, we have to develop tools to assess and predict such impacts. This paper presents methodologies to assess the current status of water resources degradation and resultant effects on human health are discussed based on some case studies.