Answer. Use of detergents is increasing day by day for cleaning purposes in houses-and industries. It is because; detergents have strong cleaning action than that of soap even in hard water. They can work even in acidic solutions. But they have a major disadvantage over the soaps, as some of the detergents are non-biodegradable (cannot be decomposed by micro-organisms like bacteria). When household water containing these detergents is discharged in streams, ponds, lakes and rivers, it causes water pollution.
The detergent remains in the water for a long time and makes the water unfit for aquatic life. The phosphate salts present in detergents causes’ rapid growth of algae in water bodies, which floats over the surface of water. These plants ultimately die and decay. Decaying plants being bio-degradable consume O2 present in water. Thus, depletion of O2 results in death of aquatic life.
Domestic sewage contains a wide variety of dissolved and suspended impurities. They include food and vegetable waste, garbage, cans, bottles, chemical soaps, washing powder, etc. It also contains disease causing microbes. All these substances add to
water pollution.