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Water pollution is addition of unwanted and harmful material in the water which renders it harmful for the use of human and degrades the flora and fauna around it. Indiscriminate use of water by increasing population and industrial expansion has led degradation of the quality of water considerably. Surface water available from rivers, canals, lakes, etc. is never pure. It contains small quantities of suspended particles, organic and inorganic substances. When concentration of these substances increases, the water becomes polluted, and hence becomes unfit for use. In such a situation, the self-purifying capacity of water is unable to purify the water.
Although water pollutants are also created from natural sources (erosion, landslides, decay and decomposition of plants and animals, etc.). Pollutants from human sources are the real causes of concern. Human beings pollute the water through industrial, agricultural and cultural activities. Among these activities, industry is the most significant contributor. Industries produce several undesirable products including industrial wastes, polluted waste water, poisonous gases, chemical residuals, numerous heavy metals, dust, smoke, etc. Most of the industrial wastes are disposed off in running water or lakes. Consequently, poisonous elements reach the reservoirs, rivers and other water bodies, which destroy the bio-system of these waters. Major water polluting industries are leather, pulp and paper, textiles and chemicals.
Various types of chemicals used in modern agriculture such as inorganic fertilisers, pesticides and herbicides are also pollution generating components. These chemicals are washed down to rivers, lakes and tanks. These chemicals also infiltrate the soil to reach the ground water. Fertiliser induces an increase in the nitrate content of surface waters. Cultural activities such as pilgrimage, religious fairs, tourism, etc. also cause water pollution. In India, almost all surface water sources are contaminated and unfit for human consumption. Also the overutilization of groundwater resources in India has led to groundwater depletion and also increased concentration of Arsenic in many parts of West Bengal and Bihar.
Domestic waste which includes sewage and other household waste also adds on to the pollution of water. Water pollution is a source of various water borne diseases. The diseases commonly caused due to contaminated water are diarrhea, intestinal worms, hepatitis, etc. World Health Organisation shows that about one-fourth of the communicable diseases in India are water-borne.