How does water get contaminated?

Groundwater naturally contains substances other than the hydrogen and oxygen atoms which make up H20.  When water falls as rain, it acquires dissolved gases from the atmosphere.  Groundwater also contains naturally occurring minerals and gases which are dissolved as it passes through the soils and rocks of the unsaturated zone and aquifer.

Water's natural ability to dissolve and carry materials allows it to be easily contaminated by human activities as well.  Normally, the soil is able to absorb and remove much of the contaminants from the wastes we add to it.  In fact, wastes such as manure actually improve the fertility of the soil.  However, if the soil layer is very thin, if the soil has high permeability, or if the water table is very shallow, we may exceed its capacity to handle wastes.  The excess contaminants may then be carried into the groundwater system by rainwater, melting snow or irrigation water.

Examples of human activities which may contaminate groundwater include agricultural and residential activities which involve fertilizers, pesticides and animal wastes, leaking fuel storage tanks, landfills and dumps, road salt, runoff from streets and parking lots, septic systems, disposal of sludge from municipal and industrial sewage treatment plants, and disposal of sewage from home septic systems.