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What is water pollution?

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Introduction

What is water pollution? Water pollution is one of the most serious environmental challenges. It occurs when water is contaminated by such substances as human and animal wastes, toxic chemicals, metals and oils. Pollution can affect rain, rivers, lakes, oceans and the water beneath the earth, called ground water. Polluted water may look clean or dirty, but it all contains bacteria, viruses, chemicals or other chemicals than can cause illness or even death. Impurities must be removed before such water can be used safely for drinking, cooking or washing. Some industries must clean the water before it can be used in their manufacturing processes. Water pollution has become a serious problem in most countries. As a result, governments have passed laws limiting the amounts and kinds of wastes that can be dumped into water. In many parts of the world, cities and towns release untreated sewage into rivers, lakes and coastal waters. Also, pollution that does not come from a direct point, such as a sewerage outlet or factory drain, is largely uncontrolled. Sources of water pollution There are three main sources of water pollution. ...read more.

Middle

* Agricultural chemicals and wastes. Water from rain or melted snow flows from farmland into streams, carrying chemical fertilisers and pesticides that farmers have used on the land. Animal wastes also can cause water pollution, particularly from feed lots with many animals. Cattle, sheep and poultry raised on feed lots do not distribute their wastes over widespread pastureland. Instead, much of their wastes runs off into nearby streams. Water used for irrigation also may be polluted by salt, agricultural pesticides and toxic chemicals on the soil surface before it flows back into the ground. Effects of water pollution * Health. Water polluted with human and animal wastes can spread typhoid fever, cholera, dysentery and other diseases. Though the water supplies are disinfected with chlorine to kill disease-causing germs, it does not remove harmful chemical compounds, such as polychlorinated biphenyls (PCB's) and chloroform, or harmful metals, such as arsenic, lead and mercury. The careless release of such toxic wastes, primarily into waste dumps, threatens ground water supplies. Scientists are concerned that drinking even small quantities of these substances over many years may have harmful effects. ...read more.

Conclusion

An excess of nutrients causes the growth of higher-than-normal numbers of plants, such as pondweeds and duckweeds, plantlike organisms called algae, fish and other animals, and bacteria. As more grow, more also die and decay. Because the decay process uses oxygen, the additional decay uses up more of the oxygen in the water. Thus, less oxygen becomes available to support living things in the water. Thermal pollution can also reduce the amount of oxygen dissolved in water. In addition, the warmer-than-normal water can kill some kinds of plants and fish. Control of water pollution * Sewage treatment. The most efficient sewage treatment plants use three processes- primary, secondary and tertiary treatment. Primary and secondary treatment can remove up to 95 percent of the waste in sewage. Tertiary treatment removes even more impurities. Many plants use primary and secondary processes, and some use tertiary processes as well. However, most treated sewage still contains nutrients and toxic chemicals because secondary processes cannot remove them all. * Pretreatment of wastes. Industries can reduce pollution by treating wastes to remove harmful chemicals before dumping the wastes into water. Industrial wastes can also be reduced by using manufacturing processes that recover and reuse polluting chemicals. ...read more.

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