Water constitutes more than 70% of the total earth's-surface. Out of the
total water resources only 2.7%, which is fresh water, is used by human
beings for themselves or for agriculture and animal husbandry. Marine
water is not uniformly available over the. different parts of the
earth. Even at a particular place the demand and availability of fresh
water differs according to season and climate. The demand for fresh
water is likely to increase with the rising population, so it is
essential to conserve this natural resource through proper management.