Where does groundwater come from?

Groundwater is an important part of the water cycle. It comes from rain, snow, sleet and hail that soak into the ground. The water moves down into the ground because of gravity, passing between particles of soil, sand, gravel, or rock, until it reaches a depth where the ground is filled, or saturated, with water. The area that is filled with water is called the saturation zone and the top of this zone is called the water table. The water table may be very near the ground’s surface or it may be hundreds of meters below.

Although groundwater exists everywhere underground, some parts of the saturated zone contain more water than others. An aquifer is an underground formation of permeable rock or loose material which can produce useful quantities of water when tapped by a well. These aquifers may be small, only a few hectares in area, or very large, underlying thousands of square kilometers of the earth’s surface.

Even if groundwater is not used by people, it may still play an important role in the local environment and sustain rural livelihoods that way. Plants may tap into it with their roots and animals may drink it when it comes to the surface as springs.

If groundwater is underground, how do we get it out?
Under natural conditions water in aquifers is brought to the surface through a spring or can be discharged into streams or wetlands. Water in aquifers is brought to the surface naturally by means of a spring, a borehole or can be discharged into lakes, streams or the ocean. We as humans can abstract groundwater through a borehole which is drilled into the aquifer.
Once a successful borehole has been drilled, we can equip it with any of the following equipment: (the choice is influenced by the specific intended use of the water, e.g. for drinking water, water supply to municipality, irrigation and other):
handpump – especially if yield of borehole is low, mainly in rural areas,
windpump – mainly on farms, can maintain higher yields,
electrical pump/diesel pump – usually when borehole yield is higher, higher assurance supply, or
playpump – effective when borehole yield is low, mainly for water supply at schools. (read more / watch the video about this innovative design at http://www.playpumps.org)
 
Boreholes require sophisticated technology with the right appropriate technical design, together with proper knowledge of the aquifer. Unfortunately, the importance of good quality borehole design and construction is often underestimated. The lifetime of a borehole and the efficiency of its functioning depend directly on the materials and the technology used. Borehole “failure” is often not linked to aquifer performance, but to the incorrect design and construction of the hole.