Reviewed October 1993

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WQ23, Groundwater Quality

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Groundwater Quality

Daryl Buchholz
Department of Agronomy

What is groundwater? Why is it important?

Water is the most important resource to man. It is essential for the existence of all forms of life. Although an ocean of water covers the earth, it is important to remember that there is no new water. The earth only contains and redistributes a certain amount.

Groundwater is water below the earth's surface in rock, sand, gravel and soil. The rainfall that enters the ground keeps up the water level. Surface water and groundwater are the two main sources for drinking water. Nearly 50 percent of the U.S. population and 95 percent of rural homes depend on groundwater for their drinking and water supply.

We need clean, usable groundwater to maintain a large and safe supply of drinking water. So we must manage our groundwater wisely so that it does not become polluted by man's activities.

How can groundwater become contaminated?

Several sources can contaminate groundwater:

  • Nature can contaminate groundwater by dissolving rocks and minerals that create very high salt content in groundwater, making it undrinkable. Shallow groundwater may become contaminated with bacteria or pathogens, and as organic matter decomposes, with nitrates.
  • Agriculture can contaminate water with waste from animal feedlots or confinement areas and with agricultural chemicals such as plant nutrients and pesticides.
  • Industry and municipalities contaminate groundwater with wastes, runoff and sewage disposal.
  • Household septic systems can contaminate groundwater.

Groundwater or well contamination?

Well water contamination can be caused by the sources listed above. However, well water may only be contaminated locally. Contamination comes through the walls of the well. Groundwater contamination implies a much larger land area as a contaminate source. People who work with groundwater quality usually use two broad terms to describe the origin of these sources of pollution.

  • Point sources
    Contaminants originating and traceable to a single source, such as a leak or spill area, a leaking underground tank or a septic system near the wellhead.
  • Nonpoint sources
    Contaminants that cannot be traced to a single source. Examples include nitrates, which may originate from livestock, chemical fertilizers and natural occurrences in the soil.
This publication was written by Karen DeFelice, former associate extension agronomist; Nyle Wollenhaupt, former state extension agronomist; and Daryl Buchholz, state extension agronomist. This material is based upon work supported by the United States Department of Agriculture, Extension Service, under special project number 89-EWQI-1-9203.

WQ23 Groundwater Quality | University of Missouri Extension