Following are the sources of water pollution:

(i) Sewage: It includes organic wastes contributed by food-processing plants, dairy farms, poultry farms, breweries, tanneries, etc. Animal excreta discharged in fields or dumped into pits reaches water bodies through run off.

(ii) Industrial waste: It includes harmful organic and inorganic chemicals that are released by different industries and effluent mills into water bodies.

(iii) Synthetic soaps and detergents: Houses and some factories discharge water containing soaps and detergents.

(iv) Solid particles: Tiny suspended soil particles that are carried to water bodies through rain cause turbidity.

(v) Thermal pollution: Hot water discharged from industries and thermal plants into water bodies alters the temperature and reduces the oxygen concentration in water.

Following are the harmful effects of water pollution:

(i) Water polluted by various pathogens can cause human diseases such as cholera, typhoid, jaundice, dysentery and hepatitis.

(ii) Water pollutants disturb the ecological balance of water bodies by promoting the growth of certain life forms that are harmful to other life forms.

(iii) Increase in the concentration of organic pollutants causes an increase in the bacterial population, which uses the available oxygen. The lack of oxygen kills fish and other animals.

(iv) Discharge of untreated industrial wastes rich in heavy metals, acids and alkalis results in the death of useful microorganisms that contribute to the self-purification process of water bodies.

(v) Thermal pollution causes a sudden marked change in the temperature of water bodies that may kill the larvae of various animals and affect the breeding of aquatic animals.