E. coli 0157:H7 and Drinking Water from Private Wells

What is Escherichia coli O157:H7?

E. coli O157:H7 (Ee KOE-lye) is one of the hundreds of strains of the bacterium Escherichia coli. Most strains are harmless and live in the intestines of healthy humans and animals. However, this strain, O157:H7, produces a powerful toxin that can cause severe illness. The bacteria can be found on a small number of cattle farms and can live in the intestines of healthy cattle.

For more information about E. coli illness and treatment, please visit CDC's E. coli website.

Where and how does E. coli O157:H7 get into drinking water?

E. coli O157:H7 is most commonly found on a small number of cattle farms where the bacteria can live in the intestines of healthy cattle. Millions of germs can be released in a bowel movement from an infected human or animal. E. coli O157:H7 may be found in water sources, such as private wells, that have been contaminated with feces from infected humans or animals. Waste can enter the water through different ways, including sewage overflows, sewage systems that are not working properly, polluted storm water runoff, and agricultural runoff. Wells may be more vulnerable to such contamination after flooding, particularly if the wells are shallow, have been dug or bored, or have been submerged by floodwater for long periods of time.

How can I find out whether there is E. coli O157:H7 in my drinking water?

If you suspect a problem and your drinking water comes from a private well, you may contact your state certification officer for a list of laboratories in your area that will perform tests on drinking water for a fee.

How do I remove E. coli O157:H7 from my drinking water?

To kill or inactivate E. coli 0157:H7, bring your water to a rolling boil for one minute (at elevations above 6,500 feet, boil for three minutes) Water should then be allowed to cool, stored in a clean sanitized container with a tight cover, and refrigerated. Currently, there is no filter certified to remove bacteria from water. This issue is being studied.

You may also disinfect your well; contact your local health department for recommended procedures. Remember to have your well water tested regularly, at least once a year, after disinfection to make sure the problem does not recur.