The Facts About Coliform Bacteria in Your Water

October 3rd, 2012

Occasionally, municipal water suppliers will report that coliform bacteria are present in the drinking water supply. Many of us wonder, though, exactly what are coliform bacteria?


Coliform bacteria are actually a group of bacteria that naturally occur in soils, surface water, and on plants but can also be normal inhabitants of your digestive system as well as the digestive systems of most warm-blooded animals. Most of the members of this group cannot make you sick.

Coliform bacteria are an indicator of water quality. Testing for all types of disease-causing bacteria is very time-consuming and costly. A much faster and more cost-effective approach is to test for the presence of all coliform bacteria, or total coliforms. This serves as a screening process for all coliforms as well as any disease-causing organisms. If  coliform bacteria are detected in your water supply, environmental contamination has occurred.  It is possible that disease-causing bacteria, viruses, or parasites may have also entered the system. The likelihood that you will get sick is relatively low but your water supplier must notify you within 30 days of the contamination. Your supplier will also then test for fecal coliforms.

Fecal Coliforms

Fecal coliforms are a sub-group of coliform bacteria. This microbe group, which includes the well-known bacteria, E. coli, is found in human and animal digestive tracts and feces. While many species of fecal coliforms are harmless, certain strains can make you sick if you ingest contaminated water. Usual symptoms include diarrhea, nausea, abdominal cramps, and headaches which will typically last for five to 10 days. E. coli O157:H7 is a particularly troublesome strain that causes severe, often bloody, diarrhea, abdominal pain, and vomiting. Small children and adults with weakened immune systems may even experience kidney failure.

If fecal coliform are detected in your water supply, it is likely that feces or sewage waste has contaminated the water system which is a concern for human health. If this occurs, your water supplier must notify you within 24 hours and you will be instructed to boil any water prior to cooking or drinking, or to only use bottled water, until the contamination issue is addressed.

Are Coliform Bacteria in Your Water?

If you would like to know whether any coliform bacteria were detected in your municipal water supply, you can view your Consumer Confidence Report which is released annually. For more information about discovering what is in your tap water, read our blog about drinking water quality. If you have a private well, the CDC recommends that you have your well tested for total coliforms every year.


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