Beneath the land areas the ground water occurs in three zones :
Zone of aeration
Zone of saturation
The zone of aeration extends from the ground surface down to the capillary fringe .This is the unsaturated zone in which
The pore spaces of the rocks are partially filled with water and air .The rain water moving vertically downward to the water table ,passes through this zone .A certain amount of water is always present in there spaces of rocks in this zone due to the molecular attraction .All the water existing in this zone is called vadose water and the zone is also called vadose zone.
The capillary fringe exist between zone of aeration and zone if saturation .The water in this zone is connected with the zone of saturation and rise above due to capillary forces.In coarse grain soil the capillary water rises only few centimeters above the water table but in fine soil or clay it may be up to a height of 10 to 15 km.
Zone of saturation is extends from the water table .In this zone all the pore spaces of the rocks are completely filled with water .As the opening in the rocks decreases with depth ,the lower limit of zone of saturation is commonly found within
A few hundreds meter of the earth surface.