Ground water as it moves through soil and rock is actually being
naturally filtered. Some substances like sand can help filter pollutants
and particles easily. Clays in soil and rock also act as a way to
"capture" and exchange some elements and compounds when they
are dissolved in water. This helps to eliminate other pollutants that
filtration cannot handle.
Water is stored in aquifers, which have similar
characteristics of reservoir rocks that store soil and gas. Well-sorted
sediments with high porosity (A) and highly fractured (C)
rocks are excellent candidates for aquifers. If poorly sorted rocks are
partially cemented (B), they are not good reservoir rocks. The fluid
must have room to move around. An aquifer is not an underground river,
it just retains the water until it is pumped out through a well or
naturally emerges as a spring.