What Are Total Coliforms?

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Total coliforms is a term used to measure the amount of coliform bacteria in drinking water and other substances consumed by humans. Coliforms are a large class of micro-organisms that are found in human and animal fecal matter and are used to determine whether the drinking water or other substance may have other disease-causing organisms in it. Water with a high total coliform level has a high probability of contamination by protazoa, viruses and bacteria that may be pathogenic.

The Total Coliform Rule (TCR)

Set by the United States Environmental Protection Agency in 1989, the Total Coliform Rule outlines both healthy goals and legal limits for total coliforms in drinking water. The rule also mandated that drinking water facilities routinely test their water for coliforms and outlined what sort of tests should be used. The Total Coliform Rule set the healthy goal for total coliforms at zero, since any coliforms present in drinking water could mean that the water is contaminated. Legal total coliform limits are set at not more than 5 percent of the total samples tested within one month.

About Coliforms

Coliforms are mostly harmless bacteria that live in the digestive systems of humans and animals. But since coliforms are often found alongside dangerous pathogenic bacteria like E. coli, their presence often means that water has been contaminated. Instead of testing drinking water for the large number of potentially dangerous bacteria and other micro-organisms that can be transmitted through fecal matter, the presence of coliforms is tested instead.


When coliforms are found in drinking water, the water treatment system is not working properly or the water has been contaminated by an outside source. When water tests find high total coliform levels, the system must be inspected, upgraded or repaired and the water must be tested for more virulent strains of disease-causing pathogens.

Worldwide Applications

Testing of total coliforms is used worldwide to measure the safety and possible contamination level of both drinking water as well as natural water sources such as rivers and lakes. According to the Food and Agriculture Organization of the United Nations, 45 percent of 110 rivers tested worldwide contain fecal coliform levels that exceed standards set by the World Health Organization (WHO).