What is a total coliform positive or present sample?

A water sample is present for total coliform or total coliform positive if coliform bacteria are found in the sample. Generally, coliforms are bacteria that are not harmful and are naturally present in the environment. They are used as an indicator that other, potentially harmful, fecal bacteria (indicated by the E. coli species) could be present. If any routine or repeat sample is total coliform positive or present, the system (i.e., the lab) must further analyze that sample to determine if E. coli are present. E. coli is a more specific indicator of fecal contamination and is a potentially more harmful pathogen than other bacteria typically found in the total coliform group. The presence of coliform bacteria in tap water suggests that there could be a problem with existing equipment or treatment systems, contamination of the source water or a breach in the distribution system that could introduce E. coli contamination.

Role of coliforms in detecting contamination

Unfortunately, specific disease-producing (pathogenic) organisms present in water are not easily identified. It would be very difficult, expensive, and time consuming to monitor for them. For this reason, it is necessary to select an easily measured “indicator organism,” whose presence indicates that pathogenic organisms may be present. A group of closely related bacteria, the total coliform, has been selected as an indicator of harmful organisms in drinking water.