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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Coliform Bacteria


Page Index

Health Effects of Total Coliform

Revised Total Coliform Rule (RTCR)

Maximum Contaminant Level (MCL)

Source Protection

Frequently Asked Questions

Additional Resources

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, known more simply as E. coli, is one type of fecal coliform bacteria. 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.

Because it would be difficult, if not impossible, to test for every disease-causing microorganism, coliforms are used as 'indicator organisms'; if coliforms are present, there is a chance harmful organisms are also present. Although not all coliform bacteria are necessarily harmful, when they are present, it is an indication that disease-causing microorganisms such as E. coli, or other bacteria, viruses, and parasites may have entered the water supply or system.

Venn diagram showing Total coliforms, Fecal coliforms, and E. coli

Total coliforms are present throughout the environment. They are found in soil, water, and human or animal waste.

Fecal coliforms are a group of bacteria within the total coliforms and are present in the gut and waste of warm-blooded animals.

E. coli is a specific species of fecal coliform bacteria. It is the best indicator of fecal pollution. Only rare strains of E. coli can cause serious illness.


Health Effects of Total Coliform

Total coliforms do not pose risks to human health. They are used to indicate whether other potentially harmful bacteria may be present. Fecal coliform and E. coli are bacteria that, when present, indicate that water may be contaminated by human or animal wastes. Some species of E. coli may result in illness, including diarrhea, cramps, nausea, headaches, or other symptoms. Children under five years of age, those with compromised immune systems, and the elderly are particularly susceptible to illness.

Fact Sheet: E. coli in Drinking Water (PDF)


Revised Total Coliform Rule (RTCR)

The RTCR is a change to the EPA’s 1989 Total Coliform Rule and was enacted to provide greater public health protection. The revised rule establishes a maximum contaminant level (MCL) for E. coli and uses E. coli and total coliforms to initiate a "find and fix" approach to address potential fecal contamination of the distribution system. It requires public water systems to perform assessments to identify sanitary defects and take corrective action.

Learn more about the RTCR


Maximum Contaminant Level (MCL) for Total Coliform

The Environmental Protection Agency (EPA) establishes health standards for contaminants in drinking water. The heath standard (Maximum Contaminant Level, or MCL) for total coliform in drinking water established by the EPA is zero. Water systems are required to take samples for total coliforms based on the population served, source type, and vulnerability to contamination. No more than 5% of samples for total coliforms can be positive in one month. (For systems that collect fewer than 40 routine samples per month, no more than one sample can be total coliform-positive per month.) If a sample tests positive for total coliforms, the system must collect a set of repeat samples within 24 hours, and analyze for E. coli.


Protecting Your Drinking Water Source from Contamination

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/or,
  • Improper well location and/or construction.

If your well has one or more of the problems described above, it should be immediately corrected. Contact your Public Water System Inspector for assistance, or call the Drinking Water Program at (207) 287-2070.

Learn more about Source Water Protection

Learn about the DWP's financial assistance options for surface water/wellhead protection and sanitary seal well caps.


Frequently Asked Questions


Additional Resources

Updated 2/10/2023