Coliform Bacteria in Water

What is coliform and why should its presence in water be of concern?

Coliform is a family of bacteria common in soils, plants and animals. The coliform family is made up of several groups, one of which is the fecal coliform group, which is found in the intestinal tracts of warm-blooded animals including humans. The presence of fecal coliform in drinking water or at swimming sites is evidence that human or animal waste has been or is present. This may be cause for concern because many diseases can be spread through fecal transmission.

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What are the negative health effects of drinking or swallowing water that contains coliform bacteria?

Coliform or other bacteria in drinking or swimming water will not necessarily make you ill. However, since these organisms are present, other disease-causing organisms may also be present. Health symptoms related to drinking or swallowing water contaminated with bacteria generally range from no ill effects to cramps and diarrhea (gastrointestinal distress).

Two common waterborne diseases are giardiasis and cryptosporidiosis; both cause intestinal illness. E. coli 0157:H7 has also been associated with drinking contaminated water and can cause intestinal illness. In very rare cases, it can cause hemolytic uremic syndrome, a serious kidney condition.

The bacterial tests performed at the Vermont Department of Health Laboratory do not detect giardia or cryptosporidium, or specify which strains of E.coli are present.

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What do coliform water tests measure?

The laboratory test for bacteria has two steps. The first step is the analysis for "total coliform," which determines if coliform bacteria are present.

If the result shows "total coliform" bacteria, the same sample is checked again, this time to determine whether the coliform bacteria in the water is of fecal origin. This result indicates whether recent animal or human waste has entered the water. The result specifically states whether E.coli bacteria have been detected.

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How much coliform is acceptable in swimming areas?

Rainfall and snowmelt wash coliform bacteria into our waters and the presence of fecal material in lakes, ponds and rivers is to be expected. Coliform bacteria are live organisms, however, and they can multiply rapidly or die off quickly, depending upon water temperature and other variables.

When the level of coliform increases to a point where the water is considered contaminated, swimming should be banned and action should be taken. In Vermont, the health protective level of E.coli bacteria in recreational water is set at 235 organisms per 100 ml of swimming water. E. coli levels above this in swimming water could mean that other disease causing microorganisms are present.

Learn more at Healthy Recreational Waters.

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How much coliform is acceptable in drinking water?

Any coliform presence in drinking water is cause for action. Groundwater in a properly constructed well or spring should be free of coliform bacteria. If coliform is found in a well or spring, it generally means that surface water has somehow leaked into the water. This could happen if rain runoff or snowmelt makes its way into the well or spring through cracks in ledge outcroppings, gravelly soil, or sandy soil. It could also be due to poor construction or cracks in the well or spring casing.

Coliform bacteria may enter the water supply if rain or snow runoff pools around the well or spring casing, if the well or spring cover is not airtight, or if the pipe leading to the house is not properly inserted and welded or grouted into the well or spring. In addition, insects, snakes, mice or other creatures getting into the well or spring can cause contamination.

Improperly maintained treatment devices also can be a source of contamination. Home water filters and other water treatment devices should be changed and maintained in accordance with manufacturer's recommendations. The presence of any fecal coliform in drinking water is of immediate concern as many diseases can be spread through fecal transmission. The risk of illness dictates that the water must be boiled to kill the organisms before it is safe to drink.

For information about dealing with such problems, see our Safe Water Resource Guide.

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How often should coliform tests be conducted?

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