Coliform Bacteria in Private Well Water and Health

coliform bacteria in private well water

Exposure and Risk

We are in contact with millions of bacteria every day and nearly all of them are harmless. Yet some of these small organisms are responsible for waterborne illnesses. Coliforms are one group of mostly harmless bacteria that live in soil and water, as well as the intestines of animals. The presence of total coliforms in drinking water can indicate that more dangerous germs, particularly fecal coliforms, have contaminated the water.

The most common source of bacteria is the soil surrounding the well. Fecal bacteria in drinking water are usually the result of contamination by a nearby sewer, septic tank, feedlot or animal yard. Bacterial contaminants may also be introduced into a well during construction or repair.


It is recommend that every private well used for any drinking water purpose be tested annually for bacteria. The local environmental health office can answer questions or assist with testing a private well for bacteria.