Groundwater is the water located beneath the earth's surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock become completely saturated with water is called the water table. Groundwater is recharged from, and eventually flows to, the surface naturally; natural discharge often occurs at springs and seeps, and can form oases or wetlands. Groundwater is also often withdrawn for agricultural, municipal, and industrial use by constructing and operating extraction wells. The study of the distribution and movement of groundwater is hydrogeology, also called groundwater hydrology.
Typically, groundwater is thought of as liquid water flowing through shallow aquifers, but, in the technical sense, it can also include soil moisture,permafrost (frozen soil), immobile water in very low permeability bedrock, and deep geothermal or oil formation water. Groundwater is hypothesized to provide lubrication that can possibly influence the movement of faults. It is likely that much of the Earth's subsurface contains some water, which may be mixed with other fluids in some instances.
The occurrence of ground water in the State is primarily confined to five alluvial regions namely (I) Piedmont deposits of outer plain of Jammu, (ii) Dune belt in the outer Himalayas, (iii) Isolated valley fill deposits in lesser Himalayas, (iv) Fluvio-lacustrine deposits in Kashmir valley and Moraines and Fluvio-glacial deposits of Ladakh. The piedmonts can be further divided into Kandi and Sirowal belts. Ground water, except Kandi area where deep water table conditions occur, is both under phreatic and confined conditions. Ground water potential in the Dune belt is limited and yield of wells, 80 to 130 m deep is 3-6 m3/hr. In isolated valley fills, the yield from confined aquifer is about 3 m3/hr. from well of 65 m depth. Dug wells in Kashmir valley have limited yield whereas deep tube wells yield between 17-216 m3/hr. Ground water occur as perched water table and gives rise to spring or unconfined conditions in Moraines and fluvio-glacial deposits. In these areas, yield of tube well varies from 36-54 m3/hr. The ground water in hard rock of Jammu region is confined to weathered residuum, where the tube wells go dry during summer seasons. The quality of ground water is generally potable.
(Data Source: www.cgwb.gov.in/gw_profiles/st_JandK.htm)