Drinking Water Analysis - Microbiology
Total Coliform, Fecal Coliform, E-coli Numeration, Heterotrophic Plate Count
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All the tests listed above are a form of analysis for microbial pollutants that can potentially be harmful to the health of individuals.
Total coliform bacteria are used as an indicator for potentially disease causing microbial pollutants. They are members of the family Enterobacteriaceae. Coliform bacteria do not necessarily cause disease but their presence in water can demonstrate that a contamination pathway does exist. Coliform bacteria persist in water longer than most disease causing organisms so the absence of coliform bacteria leads to the assumption that the water is safe to drink. Consuming water with coliform bacteria may cause gastrointestinal illness and other flu like symptoms. People with suppressed immune systems will be most at risk. The Safe Drinking Water limit for bacteria requires that no coliform bacteria be observed in the water.
Fecal coliform bacteria are part of the coliform family. Drinking water samples should be tested for fecal coliform if the sample is positive for total coliform. Fecal coliform bacteria are naturally found only in the gastrointestinal tract of warm blooded mammals.
CWM Environmental is certified to test for Total and Fecal coliform by two methods. The first is by SM 9222B which is a membrane filtration method. The second and most commonly used method is by Colilert utilizing SM 9223. This method uses hydrolysable substrates for the simultaneous detection of the enzymes of total coliform and E. coli. Standard Methods defines Total coliforms using the chromgenic technique as all bacteria that possess the enzyme Beta-D-galactosidase, which cleaves the chromogenic substrate resulting in the release of chromogen. This release of chromogen changes the color of the sample identifying it as positive. The presence of E. Coli in the water sample results in a different enzyme which results in the release of a fluorogen. This can be observed by the use of an ultra violet light.
Heterotrophic bacteria are a more general indicator of bacterial contamination. The method, SM 9215 B, is a procedure for estimating the number of live heterotrophic bacteria in water and measuring changes during treatment. This test measures all bacteria including coliforms. The limit for Heterotrophic bacteria is 500 per 1 ml of sample.
E. Coli enumeration is a specialized test required of all public water suppliers who use surface water as the source for their water supply. The testing is required by the USEPA under the Long-Term 2 Enhanced Surface Water Treatment Rule (LT2, for short). The water supplier must test the raw source water every other week for a year. The average E. coli density per 100 mL of water is then calculated; if the average is above a threshold established by the USEPA, then the supplier must test the raw water for the presence of cryptosporidium cysts. If the raw water is found to be non-compliant with EPA regulations, then the supplier must provide additional treatment of the water in order to ensure that a safe supply is delivered to the public.
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