There are three groups of coliform bacteria. Each is an indicator of drinking water quality and each has a different risk level. Total coliform is a large collection of different forms of bacteria. Fecal coliform are types of total coliform that exist in feces. E. coli is a subgroup of fecal coliform. Labs test drinking water samples for total coliform. If total coliform is present, the lab also tests the sample for E. coli.

Total coliform bacteria are common in the environment (soil or vegetation) and are generally harmless. If a lab detects only total coliform bacteria in drinking water, the source is probably environmental and fecal contamination is unlikely. It is important to find and resolve the source of the contamination.
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Public Water System
​When coliform bacteria are found, water systems investigate to find out how the contamination got into the water. They collect additional water samples and inspect the entire system to locate the problem area. Collecting additional samples helps determine whether an actual problem exists. If the lab gets a present result on bacteria on the additional samples, it validates that there is an issue. If total coliform bacteria is present in your drinking water, your water system must conduct an assessment to find out how the contamination got into the water. If the assessment identifies the cause of the contamination, the water system can usually correct the problem with repairs, treatment, or improved operation and maintenance practices. When a lab confirms total coliform bacteria in drinking water, we recommend that the water system notify its customers as soon as possible. The notice will explain what the system is doing to correct the problem, when the problem will likely be resolved, and what customers may need to do until then.