What is the testing method used to detect bacteria in drinking water?
A. The method used by the Monterey County Health Department’s Public Health Laboratory is a present/absent test called Colilert®, from IDEXX Laboratories. This process involves adding a reagent powder to a 100 mL sample and incubating for 24 hours. After incubation, a color change to yellow indicates a positive result for total coliform bacteria (a group of normally benign organisms commonly found in plant and soil material, that act as an indicator for potentially hazardous organisms, such as E. coli). Once a total coliform positive result is confirmed, the sample container is then taken to a darkroom where it is exposed to UV light. If the sample fluoresces, then it is also present for E. coli bacteria. No color change, after the 24-hour incubation period, indicates an absent result for both total coliform and E. coli. This testing method does not identify individual strains, nor does it calculate a number to indicate the severity of the contamination. The Colilert® test only determi
