Life is possible on earth due to the presence of water. Nearly three-fourths of the earth's surface is covered with water. Water is also found below the earth's surface. It is present in air in the form of water vapour. About 70 per cent of the human body is water. The bodies of all plants and animals contain water.
Sources of Water:
Rainwater, oceans, rivers, lakes, streams, ponds and springs are natural sources of water. Dams, wells, tube wells, hand-pumps, canals, etc, are man-made sources of water.
Rain water collects on the earth in the form of surface water and underground water (Fig. 8.1).
Water present on the surface of the earth in the form of oceans, rivers, lakes, ponds and streams is called surface water. The water in rivers and lakes comes from rain and melting of snow on mountains. Rivers flow into the sea.
Some of the rainwater seeps through the soil on to the non-porous rocks below. This is underground water. Sometimes due to high pressure, this water sprouts out in the form of springs. It can be obtained by digging wells, sinking tube wells, etc.