Two of the problems associated with water are shortage and pollution. We will discuss the cases of water shortage under the section on conservation. In this section, we will discuss the cases of pollution of surface water bodies, ground water and the seas. Water is said to be polluted if it becomes harmful for the health of living organisms. The main sources of water pollution are industrial effluents, or discharge from industries and urban sewage. Let us consider some of the major pollutants and their sources.

Disease –causing organisms

Urban sewage, and human and animal excreta washed into water bodies by rain carry disease- causing microorganisms and parasitic worms. Sewage is meant to be treated before being released into water bodies, but often it is not treated or improperly treated. Bathing, washing clothes or bathing animals in or near water bodies are other ways by which disease- causing organism is carried in to water bodies.

Chemicals

Pesticides, detergents, toxic metals like led and mercury, industrial solvents, acids, plastics and other industrial chemicals find their way into water bodies from mines, industries, crop fields and sewers. The also seep through the soil and contaminate ground water. They harm the organisms living in water bodies and pass on to others through food chains. Being no biodegradable, they persist in the bodies of these organisms and cause many problems.

Hot water

The discharges o hot water bodies by some industries, particularly power plants, causes thermal pollution. Even a small change in the temperature of water affects aquatic life.

Oxygen demanding waste

Organism waste from farms, food processing industries, poultry farms, slaughter hoses, sewage, and so on, is decomposed by bacteria living in water bodies. These bacteria use up the oxygen in the water, depriving other organisms of oxygen.

Eutrophication

The accumulation of plants nutrients in water bodies and the rapid growth f algae resulting from this is called Eutrophication. The nutrients come from organic waste and fertilizers. The algae covering the water surface cut off the supply of light other organisms. What is worse, hen the algae die, they are decomposed by bacteria, which use up dissolved oxygen and deprive other species.

Excessive growth of algae takes place in the seas too. This is referred to as algal boom and can harm marine organisms in two ways. Some algae release toxins which harm other organisms. Also, bacteria act upon the dead algae that sink, using up the oxygen supply of organisms dwelling at the bottom of the sea.

Marine pollution

Coastal waters get polluted by sewage and industrial effluents released directly into the sea. They are also polluted by pollutants carried from the shore by rainwater and rivers. Silt carried by rivers often chokes coral reefs near the shore.

One of the major sources of marine pollution is the production and transport of petroleum production. Offshore drilling for oil, oil spills from tankers carrying oil and the cleaning of tankers create huge patches of oil that float over the sea. These called oil slicks.

Ground water

Ground water is usually purer than surface water because rainwater gets filtered as it seeps through and contaminates groundwater. Thus, ground water can get contaminated by pesticides from crop fields, toxic chemicals from industrial waste dumps, leakage from sewers, seepage from sites where urban waste is disposed of, and so on. It can also get contaminated b toxic chemicals present in the layers of rocks below. Ground water in many parts of India has got poisoned by arsenic and fluorides in this manner. Drinking contaminated ground eater can lead to crippling diseases and even death.

Controlling water pollution

1) Sewage must be treated properly before being discharged into water bodies. The same goes for industrial effluents. Figure 5.7 is a schematic diagram of how sewage is treated before being released into water bodies. The sludge that settles at the bottom of the treatment tanks can be converted into organic manure.

2) Public awareness should be created about the ills of throwing waste, carcasses and religious offering into water bodies. Bathing or washing in or around sources of water, and defecating in the open. People should also be made aware of the benefits of sanitary toilets and septic tanks, and efforts must be made to construct these n places which lack sanitary facilities.

3) Agriculture chemicals should be used judiciously so tat run –offs do not contaminate water bodies.

4) Industrial and urban solid waste should be disposed of properly so that harmful chemicals and other pollution do not seep through his soil or get washed off into water bodies.