Division of Environmental and Community Health

Maine Center for Disease Control & Prevention

A Division of the Maine Department of Health and Human Services

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DHHSMeCDCEnvironmental and Community HealthDrinking WaterDrinking Water ConsumersColiform Bacteria

Coliform Bacteria

Coliform bacteria are microscopic organisms that are used as indicator organisms for testing drinking water quality.

Coliform bacteria make up a large group of bacteria that are found in soils, on plants, and in surface water. Certain coliform bacteria, such as fecal coliform, live in the intestines of humans and animals. Escherichia coli or E. coli is a type of fecal coliform bacteria that is commonly found in the intestines of animals and humans. When E. coli is present in water it is likely that there has been sewage or animal waste contamination. Sewage and animal waste can contain many types of disease containing organisms and consumption can result in illness.

A fact sheet with more information on E. coli in drinking water can be found here:

Coliform bacteria, often referred to as total coliform bacteria, are used as an ‘indicator’ for testing drinking water quality. Though not necessarily harmful, when present, total coliform bacteria are an indication that disease causing microorganisms such as E. coli, other bacteria, viruses, and parasites may have entered the water supply or system. Because it would be difficult, if not impossible, to test for every disease-causing microorganism, coliforms are used as an indicator organisms; if coliforms are present, there is a chance harmful organisms are also present.

You can learn more about total coliform bacteria on this page of our website.

Protecting your drinking water source from contamination

Soil particles act as a filter, removing microorganisms, as water from the surface moves downwards through the soil horizon into the ground water.

Most bacteria in wells or springs come from surface water contaminated by sewage or animal waste. As water from the surface seeps downward through the soil, microorganisms are often filtered out. The extent of the natural filtration depends on the depth and characteristics of the soil profile. In general, shallow wells and springs are more easily contaminated than deep wells. Proper location, construction, and maintenance of wells and springs can help to prevent contamination of drinking water.

The presence of coliform bacteria and/or E. coli in wells or springs usually result from:

  • Well or spring covers that allow dust, rain, bird droppings, and other material to enter;
  • Wells or springs that are located in areas where surface water covers the well or spring during the wet periods of the year;
  • Defective steel well-casing seals;
  • Shallow wells or springs with rocked up sidewalls;
  • Recent changes or repairs to the well or spring, pumps, piping, etc; and,
  • Improper well location and/or construction.

If you have one or more of the problems described above, it should be immediately corrected. Call your public water system inspector for assistance or the Drinking Water Program at 287-2070.

The Drinking Water Program has financial resources available for surface water and wellhead protection and sanitary seal well caps. Learn more about these programs on this page of our website.