Water pollution is as dangerous to health as air pollution. It takes place when effluents from factories are let into rivers. When there is no river the effluents from the factories stagnate on land. These effluents then seep slowly into the ground and pollute the underground water. Disposal of urban sewage into rivers pollutes the river water, for example, the rivers Ganga and Yamuna get continuously polluted. Since the water from these rivers is also used for domestic purposes, it causes the spread of water borne diseases like jaundice, dysentery, typhoid, etc. Effluents from a large number of tanneries in north Arcot district of Tamil Nadu have polluted well water in a number of villages. Water also gets polluted owing to the use of insecticides and pesticides in the agricultural fields. These get washed into the rivers with the rains. Ocean water gets polluted by oil spills from tankers and sewage discharge from factories located along the coast.