What is water pollution? What are the principal sources of water pollution?

Water pollution is defined as the contamination of water by foreign substances which make it harmful for the health of animals or plants or aquatic life and make it unfit for domestic, industrial and agricultural use. The principal sources of water pollution may be classified as:
(i) Organic matter
(ii) Organic chemicals
(iii) Oils
(iv) Plant nutrients
(v) Sediments
(vi) Heat
(vii) Inorganic chemicals and minerals
(viii) Pesticides
(ix) Detergents
(x) Radioactive wastes.