Surface water includes river water, lake water and pond (tank) water but here under this heading only river water pollution has been discussed. Major source of surface water is precipitation. It is polluted through the mixing of different quantities of dis­solved inorganic matter in the form of ions.

Accord­ing to a study of the NEERI seventy per cent of the available water in India is polluted. Most of the Indian rivers receiving urban and industrial efflu­ents are highly polluted. According to an estimate 300 class I cities (each with a population of more than l lakh) with a total population of 140 million (1991) generate over 10,000 million liters of sewage per day whose major portion enters the rivers with­out being treated. About 40 river basins have been badly affected by untreated city sewage. Most of the

Indian cities get a large part of their drinking water from rivers. Hence growing pollution of the rivers constitutes the biggest threat to public health. Dur­ing 1990s more than 1 million children died due to diarrhea and other gastro-intestinal diseases.