Coliform bacteria are a large group of bacteria that include fecal coliform bacteria, such as Escherichia coli (E. coli), which naturally occur in the intestines of warm-blooded animals. They can also include non-fecal coliform bacteria.
When coliform bacteria, especially fecal coliform or E. coli, are present in well water, it indicates that the water has come into contact with human or animal waste and could potentially cause disease. Coliform bacteria is listed as a primary contaminant by the USEPA because any amount of these bacteria in your drinking water can have potential health effects. It is important for people who drink water from a private well to have the water tested at least once a year to ensure its safety.
A close up of hands performing a coliform bacteria test, a fundamental aspect of water monitoring to detect potential health risks/Adobe Stock
What are the effects of coliform bacteria in well water?
While coliform bacteria are generally not harmful, the presence of fecal coliform or E. coli in water can pose health risks. Drinking water contaminated with these bacteria may cause gastrointestinal illnesses such as diarrhea, abdominal cramps, and nausea. It is important to note that the symptoms may vary depending on the individual’s immune system and the specific strain of bacteria present.
Figure 1- Fecal coliforms are a subset of total coliform bacteria. Escherichia coli (E. coli) is a subset of fecal coliform bacteria. Several strains of E. coli exist, and some, such as E. coli O157:H7, can cause serious illness./Alabama Extension
When should I test for coliform bacteria in my well water?
Signs of coliform bacteria or E. coli contamination in well water may not be apparent through visual inspection, taste, or smell. The only way to reliably determine if your well water is contaminated with these bacteria is to have a sample analyzed by a certified laboratory. To ensure you are protecting your family’s health, we have developed a set of recommendations for testing that are provided in our article, "What do I need to know about sampling my well water?, that includes coliform bacteria.
What treatment should I use if there is coliform bacteria in my well water? How do I remove coliform bacteria from my water?
If you receive a positive test result for total coliform or coliform bacteria, it is important to take immediate action. It is recommended to follow these guidelines:
Retest to confirm contamination
Collect another water sample and have it screened or tested specifically for fecal coliform bacteria or E. coli to get an accurate result. If you are taking the sample yourself, ask the professional providing the sample bottles for advice on best practices.
Do not drink the water
Use bottled water for drinking and cooking until the results from the second water test are received. If bottled water is unavailable, boil the water used for drinking, cooking, and brushing teeth to make it safe.
Find the source and fix the problem
Possible causes of contamination include faulty wellhead or improper well construction, shallow well near surface water, old or unused wells, septic systems, or other sources of contamination nearby.
Disinfect your well
Once the source of contamination has been fixed, look at the article, "How do I disinfect (bleach) my well?" for directions.
Where can I get local help and information about coliform bacteria in my well water?
Contact your local health department – They can help you interpret your sample results and may have information on the best treatment options for your situation. If they personally aren’t able to answer your questions, they will know who to contact who will be able to help you, likely at your state health department.
State or Federal Geologic or Water Resource Agency – they may have completed field studies of your area or collected samples from water wells to map and understand the water quality in your state. In addition, they may house water well logs, including yours, or be able to provide additional information about the aquifer your well is getting water from.
Consult your well driller or drilling contractor – the contractor that drilled your well, and other local contractors, may be aware of the water quality issues nearby including high iron, and might have worked with other well owners in your area to solve this issue .
Research online – you should be inquisitive; it will help you significantly because there may be great information available online. Use search terms like “my state (CA, ME, IL, etc.) water well logs”, “my state groundwater quality”, or “my state well water quality”.
Contact us directly – if these other local sources don’t work out for you, we may be able to help. We may be able to provide direct assistance, and/or direct you to a technical assistance provider in your area who can help answer your questions (free service funded by USEPA).
Additional Resources
Coliform and Nitrate Information for Private Well Owners, May 2010, Washington Department of Health.
How to Sample Well Water for Coliform Bacteria with Ray Kline, CMI®-International Association of Certified Home Inspectors
Want to learn more about your private well and how to care for it?
Sign up for the free 10-week email course from PrivateWellClass.org. The class is a project of RCAP and the University of Illinois, with funding from USEPA.
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