The chief sources of water contamination throughout the world are (1) sewage and other waste, (2) industrial effluents, (3) agricultural discharges and (4) industrial wastes from chemical industries, fossil fuel plants (thermal power plants) and nuclear power plants. Each of these sources of pollution carries a variety of pollutants that enter our water bodies.
One of the most common primary sources of water pollution is the discharge of untreated sewage in water bodies, some times due to improper sewage-handling processes of municipal bodies.
Agricultural discharge sources include chiefly the chemicals used as fertilisers and the pesticides used in disease control. Their discharges reach into the water bodies.
The two chief industrial wastes are heat and radioactive substances. These have adverse effects on aquatic life.