Aquifer is defined as a rock mass, layer or formation which is saturated with groundwater and which virtue of its properties is capable of yielding contained water at economical costs when tapped.

All rocks are neir capable nor suitable for holding and transmitting groundwater. The terms like aquifer, aquiclude, aquifuge need to be understood well for studying concept of groundwater.

An associated trouble with rising water-table is development of salinity of soils. The rising groundwater may be rich in some undesirable salts that are left at or near surface during its loss to atmosphere due to evaporation.

The porosity of limestones varies from 1 to 20%. Hydraulic conductivity in highly karsted limestones may be as high as 100 m/day or even more, to be classed among extremely permeable rocks.

Vadose water, which occurs from surface downwards up to a variable depth and is in a state of downward movement under influence of gravity.

Artesian aquifer is, in fact, confined aquifer of such a geometry developed in suitable geological situations so that mezometric surface is always above ground level at many places when projected in elevation.

Perched water table is term used for isolated water table in an aquifer held by a small extension of impervious rock within a large pervious tract.

This connate water may be encountered in sedimentary rocks like limestones, sandstones and gravels. It is commonly saline in nature and is of no importance as a source for exploitable groundwater.

As a storage reservoir, aquifer behaviour is controlled by- nature of rock and its porosity, structural disposition, with regard to recharge points or places, climate conditions like annual precipitation.

Juvenile water is also called magmatic water and is of only oretical importance as far as water-supply schemes are concerned.