Coliforms and E.Coli in Well Water


When performing a water test for microbiological contamination of well water, the indicator that’s most often used is “Total Coliforms”.   Coliform bacteria occur naturally in soil and decaying vegetation.  They are often indicators of he presence of human or animal fecal contamination.  Under normal circumstances, coliforms do not grow in well water because the water is cold (10c or 50F), and it is usually either alkaline (basic), or acidic (pH).  As water moves from the surface down through the ground and into the aquifer, these bacteria are usually filtered out and don’t reach it.  Unfortunately, though, once coliforms get into a well, they will survive for a very long time unless they are remove.


Escherichia Coli, or E.Coli

Many coliforms are completely harmless.  They are still indicators of fecal contamination, however, they will not make you sick.  E.coli in well water can not only make you sick, but is potentially deadly.  E.coli is found in the intestines of warm-blooded animals like dogs, cows, horses, and humans.   When a water test includes a high “Total Coliform” count, it may not include the potentially illness-causing e-coli.  If coliforms are present, though, they are a good indication that your water has been contaminated by some form of fecal matte, and should be addressed right away.

E.coli in your well water is especially dangerous for the very young, the elderly, and those who are immune-compromised.  If your water test indicates a high Total Coliform count, you are best to err on the side of caution and install some form of disinfection as soon as possible.

How did coliforms get into my well water?

There are many ways that coliforms can enter your well water.  Heavy rainfall, spring runoff, and flooding events are often high on the list of causes – overwhelming even newly-constructed wells, and introducing surface contaminants, including e.coli, into the well. If you have an older well, there are even more potential avenues for surface contamination (including coliforms) to enter your water.  The best way to prevent illness is to be pro-active about well stewardship, and performing regular water testing.

For more detailed information about E.Coli and the threat to human health it poses, please check out CDC Webpage on E.Coli