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