Coliform are a group of bacteria that are common in nature. Some coliform bacteria can cause illness while others do not. Drinking water should not have coliform bacteria in it. When coliform are present, the well may been contaminated by soil or feces. If a water sample shows coliform bacteria are present, the water is checked for E. coli. E. coli are a type of coliform bacteria found in the gut of mammals. When E. coli are present, the well may be contaminated by human or animal feces. Wells can become contaminated with bacteria when work is done on the well, if the well was not built or maintained properly, or if there are nearby sources of animal or human waste.

The data shows the number of samples that tested unsafe and often additional samples for the well are tested after steps have been taken to make the water safe again. This means the data may have results from the same well and doesn’t mean the this is the percentage of wells that were unsafe.  Private wells should be tested at least once each year for coliform bacteria.