How is water is polluted?

There are various reasons for water pollution:
a. Water dissolves the fertilisers and pesticides that we use on our farms. So some percentage of these substances are washed into the water bodies. b. Sewage from our towns and cities and the waste from factories are also dumped into rivers or lakes.c. Specific industries also use water for cooling in various operations and later return this hot water to water-bodies.d. Another manner in which the temperature of the water in rivers can be affected is when water is released from dams. The water inside the deep reservoir would be colder than the water at the surface, which gets heated by the Sun.