Man uses water for drinking, preparation of food, bathing, for cleaning the house, etc. Most of the used water is drained out through municipal drains and poured into a river or lake. Domestic waste water that is mixed with other wastes such as plastic, detergents, animal dung and human faecal material is known as municipal waste.
Many detergents and fertilisers contain phosphates. When phosphates are discharged into waterways, their remnants promote rapid growth of algae. Such enrichment process is known as eutrophication. Aquatic weeds multiply rapidly in many water bodies. They interfere with fishing, navigation and irrigation.