Ground water has gotten into the earth from one of the following sources:
1. Meteoric water.
2. Condensational water.
3. Connate water.
4. Juvenile water.
5. Mixed source water.
1. Meteoric Water
It includes waters formed by infiltration of atmospheric precipitation like rain, sleet, snow, hail etc. as well as by the infiltration of water of rivers and lakes.
As we know, falling on the earth’s surface, atmospheric precipitation is distributed in a number of ways-a part of the water enters the soil by infiltration, a part is returned to the atmosphere through evaporation and another part flows over the ground surface as runoff to lower levels.
Water of such origin apparently constitutes the bulk of ground water, which is evident from the fluctuation of water level in the wells with the changing of seasons.
2. Condensational Water
This water is mainly the source of replenishment of ground waters particularly in deserts and semi deserts, where precipitation is scanty and there is rapid evaporation. In such regions, there is ground water at certain depth below the surface. This is believed to be due to the following process:
The moist air at the surface of the earth is always warmer than the air of the soil, particularly in summer. Accordingly, there exists a difference in the pressure between the water vapour in the atmosphere and in the soil.
Because of the pressure gradient, water vapour from the atmosphere penetrates the rocks and are converted to water through condensation when the temperature falls. This may lead to the accumulation of a certain amount of water in rocks in arid and desert regions.
3. Connate Water
This is also known as fossil water and includes water entrapped in sediments at the time of their deposition on lake or sea bottom. They are classified in to two types as syngenetic and epigenetic connate water.
The syngenetic connate water was trapped in the sediments containing it, whereas the epigenetic connate water are those which entered from the basins into the rocks that had formed earlier. Connate water often occurs in rock units with oil.
4. Juvenile Water
It is also known as magmatic water as it is associated with the magmatic activities within the crust. With the cooling of magma, its gaseous contents and water vapour etc. separate out from it.
The water vapour then gets condensed into superheated water and move upwards from a region of high temperatures and pressures to that of low temperature and pressure. This is also called virgin water.
5. Mixed Source Water
It is quite natural to expect that along their complex-migration routes the aforesaid waters get mixed up and thus constitute ground water of a mixed type.