Water pollution is a major cause of concern in our country.

Because a very large part of the population depends directly on rivers, lakes and ground water for drinking, bathing and irrigation, while untreated SEWAGE, INDUSTRIAL EFFLUENTS and agricultural run-off are discharged into the same water bodies. This spreads water-borne diseases such as cholera, typhoid and dysentery, kills aquatic life, and makes scarce fresh water unfit for use.

A "give the reason" question wants a CAUSAL CHAIN, not a general statement that pollution is bad. Name the POLLUTANTS and the CONSEQUENCES.

Three consequences worth having ready: HUMAN HEALTH — water-borne diseases from sewage; heavy metals such as mercury and lead accumulating in the food chain AQUATIC LIFE — decomposing sewage consumes dissolved oxygen, and fertilisers cause EUTROPHICATION, both of which suffocate fish SCARCITY — India already faces falling water tables, so polluting what remains is doubly serious