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SKETCH OF SOME ELEMENTS OF EARTH'S HYDROLOGICAL CYCLE
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All water, whether captured from a stream, collected as rain, or mined from below the
surface, is recirculated to the atmosphere. This never-ending exchange of water from earth to atmosphere, accomplished through precipitation and evaporation, is known as
the hydrological cycle.
Water quality may be affected in several ways as water moves through the phases of
the hydrological cycle. For example, as water percolates into the ground it may gather contaminants from the soil that affect the quality of groundwater. Rainwater may
collect impurities from the air, and runoff from rainfall may gather impurities from the land surface, both of which can affect the surface water quality in lakes and rivers.
The overall quantity of water moving through the cycle also may change. Water used in industrial processes, for
example, may become so contaminated that it cannot be treated and returned to the cycle as wastewater, but instead
must be kept on site in impoundments. Such water would therefore be permanently removed from the hydrological
cycle. Thus, in the cycle, groundwater, surface water, and human activities are all interrelated.
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