Group B Public Water Systems - Coliform Bacteria


Coliform Bacteria in Drinking Water

Group B systems should deliver safe and reliable drinking water to their customers 24 hours a day, 365 days a year. If the water supply becomes contaminated, consumers can get seriously ill. Operators of Group B systems can take steps to make sure drinking water is safe.

One of the most important steps is testing for coliform bacteria. We recommend operators sample for coliform bacteria from their distribution system at least once a year. Use a certified lab to perform the analysis.

NOTE: If you search for labs that test for coliform by using "search for analyte," make sure you select a lab that tests drinking water.

What are coliform bacteria?

Coliform bacteria are present in the environment and feces of all warm-blooded animals and humans. Coliform bacteria are unlikely to cause illness. However, their presence in drinking water indicates that disease-causing organisms (pathogens) could be in the water system. Testing drinking water for all possible pathogens is complex, time-consuming, and expensive. It is easy and inexpensive to test for coliform bacteria. If testing detects coliform bacteria in a water sample, the system operator should search for the source of contamination and restore safe drinking water.

There are three groups of coliform bacteria. Each is an indicator of drinking water quality and each has a different level of risk. Total coliform is a large collection of different kinds 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 fecal coliform or E. coli, depending on the lab testing method.

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 from environmental sources, and fecal contamination is unlikely. However, if environmental contamination can enter the system, pathogens could get in, too. It is important to find and resolve the source of the contamination.

Fecal coliform bacteria are a subgroup of total coliform bacteria.

E. coli is a subgroup of the fecal coliform group. Most strains of E. coli bacteria are harmless. The presence of E. coli in a drinking water sample indicates recent fecal contamination and a high risk that pathogens are present.

E. coli outbreaks receive a lot of media coverage. A specific strain of E. coli bacteria known as E. coli O157:H7 causes most of those outbreaks. When a drinking water sample is reported as “E. coli present,” it does not mean that O157:H7 is present. However, it does indicate recent fecal contamination. Boiling at a rolling boil for one full minute destroys all forms of E. coli, including O157:H7.

What if coliform bacteria are found in my water?

When coliform bacteria are found, there should be an investigation to find out how the contamination got into the water. In addition to inspecting the source, storage, and distribution system, an operator of a Group B system should collect additional coliform samples from customers and from the source. Collecting additional samples helps determine whether an actual problem exists. If the lab detects bacteria in any of the additional samples, the initial findings are “confirmed.”

What if total coliform bacteria are confirmed in my water?

If a lab confirms total coliform bacteria in your drinking water, an operator of a Group B water system should more thoroughly investigate to find out how the contamination got into the water. After identifying the source of contamination, the operator can usually resolve the problem with system repairs, flushing, and adding chlorine for a short time period.

What if fecal coliform bacteria or E. coli are confirmed in my water?

Confirmation of fecal coliform bacteria or E. coli in a water system indicates recent fecal contamination, which may pose an immediate health risk to anyone who consumes the water. If E. coli is confirmed, the operator of a Group B water system must notify system consumers within 24 hours of the health risks.

We recommend that the operator of a Group B system with confirmed fecal coliform or E. coli issue a “health advisory” within 24 hours to alert all water users of a health risk associated with the water supply. Here is a public notice template (Word) you can use. The notice advises consumers to use boiled or bottled water for drinking, preparing food, and brushing teeth and explains when the system expects to resolve the problem.

More water samples should be collected to find and eliminate potential contamination sources, and the system should be chlorinated and flushed. The health advisory should remain in effect until the situation is resolved and the water is safe to drink.

Where can I get my water tested?

For a list of certified labs, visit the state Department of Ecology online.

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