Addition or presence of undesirable substances in water is called water pollution.

Water pollution is one of the most serious environmental problems. Water pollution is caused by a variety of human activities such as industrial, agricultural and domestic. Agricultural run off laden with excess fertilizers and pesticides, industrial effluents with toxic substances and sewage water with human and animal wastes pollute our water thoroughly. Natural sources of pollution of water are soil erosion, leaching of minerals from rocks and decaying of organic matter. Rivers, lakes, seas, oceans, estuaries and ground water sources may be polluted by point or non-point sources. When pollutants are discharged from a specific location such as a drain pipe carrying industrial effluents dischaged directly into a water body it represents point source pollution. In contrast non-point sources include discharge of pollutants from diffused sources or from a larger area such as a run off from agricultural fields, grazing lands, construction sites, abandoned mines and pits, roads and streets.

Out of the following which is not a cause of water pollution?

seasonal rainfall

The correct answer is Option (4) - seasonal rainfall