Coliform Bacteria | Lake Management Insights
Background/overview
Biological organisms are among the oldest health threats to drinking water quality and the agents currently responsible for most waterborne diseases. They are the most common contamination incident water operators will encounter. Organisms known to cause disease include bacteria, protozoa, and viruses; some algae and helminths (worms) may also be capable of producing disease. These disease-causing organisms thrive in the intestines of warm-blooded animals. They are easily transmitted to drinking water if the feces of an animal contaminates a water supply for which there is not suitable disinfection. Potential sources of contamination include sewers, septic systems, feedlots, and animal yards.
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.
Sources of Coliform Bacteria
Total coliform (TC) bacteria are common in the environment (such as in soil) and the intestines of animals and are generally not harmful. Escherichia coli (E. coli) bacteria are found in greater quantities than total coliform in animal fecal matter. If E. coli is detected along with TC in water, there is strong evidence that sewage is present; therefore, a greater potential for pathogenic organisms exists.
Exceptions
Total coliforms are not a perfect indicator of the actual or potential presence of harmful organisms.
