• The water absorb by the soil which percolates downwards ultimately joins the ground water reservoir.
  • It is that water which is readily available all the time.
  • It can be avail by digging wells.
  • Ground water reservoir is a big natural ‘ storage of water.
  • The part of rainfall that infiltrates into the ground percolates downwards unless checked by impervious layer.
  • Since impervious layer does not allow infiltrated water to go further down, it gets stored in the soil above the impervious layer forming ground water reservoir
  • This water remains held up in the voids of the soil.
  • The layers of soil in which water is held up in soil pores are known as water bearing formations.
  • They act as storage reservoirs for ground water and also as conduits for transmission of water.

(i) Zone or rock fracture and

(ii) Zone of rock flowage.

  • The depth of the zone of rock flowage is not known accurately.
  • Its presence is estimated to lie kilometres below the surface of the earth.
  • This zone does not contain interstices as stresses here are beyond the elastic limits and the rock remains more or less in a state of plastic flow.
  • Water present in this zone is known as internal water and a hydraulic engineer has nothing to do with this water.



  • Zone of rock fracture lies above the zone of rock flowage. Interstices do exist in this zone and water is stored in the voids.
  • The amount of water present in the voids is dependent upon porosity of the zone.
  • Zone of saturation is below the water table and the zone of aeration above the water table.
  • In the zone of saturation, water exists within the interstices or pores and is known as ground water.
  • The space above the Water Table.