Beneath most land areas the groundwater occur in three zones
Zone of Aeration in Ground Water
The zone of aeration extends from the ground surface down upto the capillary fringe. This is the unsaturated zone in which the pore spaces of the rock are partly with air. The rain water moving vertically downwards to the water table passes through this zone. A certain amount of water is always held in smaller pore spaces due to molecular attraction. All the water which exists in the zone of aeration is called vadose water.
The position of the capillary fringe is in between the zone of aeration of saturation. The water in this zone is connected with the zone of saturation and is raised above it by capillary force. In coarse grained soils the capillary water rises only a few centimeters above the water table, but in fine grained soils or clays it may rise to a height of 10-15 meters.
Zone of Saturation
This zone extends from the water table downwards. In this zone all the pore spaces of rocks are completely filled with water. As the opening in the rock decrease with depth, the lower limit of the zone of saturation is commonly found within a few hundred meters of the earth’s surface.