What
is groundwater ?
It is sometimes thought that water
flows through underground rivers or that it collects in underground
lakes. Groundwater is not confined to only a few channels or depressions
in the same way that surface water is concentrated in streams and lakes.
Rather, it exists almost everywhere underground. It is found underground
in the spaces between particles of rock and soil, or in crevices and
cracks in rock.
The water filling these openings is
usually within 100 meters of the surface. Much of the earth's fresh
water is found in these spaces. At greater depths, because of the weight
of overlying rock, these openings are much smaller, and therefore hold
considerably smaller quantities of water.
Groundwater flows slowly through
water-bearing formations (aquifers) at different rates. In some places,
where groundwater has dissolved limestone to form caverns and large
openings, its rate of flow can be relatively fast but this is
exceptional.
Many terms are used to describe the
nature and extent of the groundwater resource. The level below which all
the spaces are filled with water is called the water table.
Above the water table lies the unsaturated zone. Here the
spaces in the rock and soil contain both air and water. Water in this
zone is called soil moisture. The entire region below the water
table is called the saturated zone, and water in this saturated
zone is called groundwater.
 Groundwater
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