Coliform Bacteria
Coliform bacteria are an indicator of potential water contamination. This class of bacteria can be found in soil, on plant vegetation, and in feces of warm-blooded animals such as humans. Most coliform bacteria are harmless soil inhabitants that will not make people sick. However, some types of fecal coliforms (e.g. E. coli), which grow in the intestines of animals, may be pathogenic and can cause diarrhea, intestinal cramps, or nausea. Water samples are collected from wells and representative distribution sample locations each week and tested for coliform bacteria. The absence of coliform bacteria indicates that water is safe for consumption.
A positive total coliform test indicates that the water is potentially unsafe and is further evaluated for the presence of E. coli. If E. coli is present, it indicates that the water has been contaminated with fecal waste. Public notification including a boil water notice is issued until additional tests show that the water supply is free of E. coli. On the other hand, if a coliform-positive sample tests negative for E. coli, the location is resampled to confirm the initial test result. If the results indicate there is a potential that the system has been contaminated, the Water Utility will take immediate corrective action, and the public may be notified to boil their drinking water until additional water sample results confirm the water is free of coliform bacteria.
Routine weekly testing of water samples occurs on chlorinated water collected from wells and distribution sample sites. In addition, on a quarterly basis (once per three month period), the Water Utility collects non-chlorinated water from each operating well immediately after it is pumped out of the ground and tests these source water samples for coliform bacteria.
To ensure drinking water safety, over 200 samples are collected each month from representative locations and tested for coliform bacteria. In 2022, the Water Utility collected 2,791 distribution samples with a single sample testing positive for coliform bacteria. The low number of coliform bacteria positive samples reflects good source water quality and adequate disinfection maintained in the distribution system.
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The table below shows the number of coliform-positive samples compared to the total number of routine samples collected:
