Occurrence of Underground Water Rain water that falls on the ground and seeps below the surface through soil, crevices, joints and fissures and accumulates under the ground, is known as underground water.
The rocks which allow seepage of water are called permeable rocks, like sandstone. Rocks which do not allow seepage of water are called impermeable rocks like clayey soil, slate, marble, granite are not permeable rocks but water seeps in them through joints and fissures present in them. The seepage of water underground produces a zone of saturation. The upper limit of the zone of saturation is known as the water table. In this, all the pore spaces, joints fissures are saturated with water. This water table varies from place to place and from season to season.
Underground water may reappear as springs along joints or fissures. These springs may be hot or cold, perennial or temporary.
Importance of Underground Water:
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The underground water is a permanent source of water as the rate of the evaporation here is minimum. It is of great importance for the following reasons: (i) where the surface water is not freely available underground water is tapped by digging wells. Man uses it for domestic purposes like drinking, washing, cooking, etc.
(ii) He can irrigate the fields.
(iii) He uses it for industrial purposes like in paper, dyeing, jute and steel industries.
(iv) It sustains vegetation on land. Some of the springs have medicinal value for skin diseases and stomach problems.