Total Coliform Bacteria

A typical sample station for taking coliform
samples in the distribution system.

Every week, drinking water operators everywhere spend their morning driving from sample station to sample station, very carefully filling little 100 mL bottles with water from their distribution systems. At least once per quarter, and probably more often, they do the same thing for the water from each and every operating well in their systems. They cap the bottles, label them appropriately, and prepare them for transport to the laboratory where they will be tested for Total Coliform Bacteria. If the test is positive, then the sample will also be tested for a particular bacterium, Escherichia coli, more commonly known as E. coli. So what is a coliform bacterium and why do we test for it? Coliform bacteria are defined as rod-shaped Gram-negative non-spore forming bacteria which can ferment lactose with the production of acid and gas when incubated at 35-37°C (American Public Health Association, Standard Methods for the Examination of Water and Wastewater, 19th ed., APHA, Washington, DC, 1995). That’s a mouthful! In other words, a coliform bacterium is one that gives a positive test result; not a real meaningful definition. In theory, the coliform test is used to try and detect bacteria that may be present because of contamination by sewage or sewage contaminated water. A great many of the bacteria that live in the gut of mammals like humans are coliform bacteria. However, coliform bacteria can and do live just about anywhere; in the soil, in surface and groundwater, in and on plants, flowers and fruits, everywhere. So just because there may be a positive coliform sample doesn’t mean that the water is contaminated. It is just an indicator that there could possibly be a problem, and that you should do some investigating to see if there are any problems you weren’t aware of in your system; maybe a leak, an unprotected backflow situation, low chlorine residuals, etc. Drinking water systems are required to test for these bacteria in the distribution system by the U.S. Environmental Protection Agency’s Total Coliform Rule (TCR), and there are very specific steps that must be taken if a test result is positive, such as taking repeat samples. The TCR is currently being revised to better reflect the fact that a positive result does not necessarily mean the distribution system is contaminated. The revised rule is expected to be finalized later this year, and would go into effect in 2014. The California Department of Public Health (CDPH) requires that each well be tested at least quarterly, and there are no regulations related to a positive result. However many water companies, in an effort to more closely monitor and protect groundwater resources, have implemented monthly testing for their wells, and implement their own actions should a well test positive.

Although not necessarily indicative of any contamination, testing for coliform bacteria can be a very good tool for keeping track of the overall health and cleanliness of groundwater resources, the distribution system, and of the water we deliver to our customers. The job of taking all those samples is a very important one for system operators.