EPA Regulatory Limits for Coliform Bacteria in Drinking Water

Coliform bacteria are microorganisms that naturally live in soil, plant-life, water and the gastrointestinal tract of animals. These bacteria often do not cause illness in humans, but abnormal bacteria counts may signal that water supply is unsafe for consumption, according to the United States Environmental Protection Agency (EPA).

Potential Hazards of Coliform

• Though many forms of coliform do not contribute to illness, some forms of the bacteria -- like fecal coliform and Escherichia coli (E. coli) -- may cause gastroenteritis. Gastroenteritis, according to the EPA, causes symptoms such as diarrhea, nausea and vomiting. Reactions that are more serious can occur in those with an impaired immune system, the elderly and young children.

Total Coliform Limits

• The EPA's MCLG (maximum contaminant health goal) for total coliform levels is zero. The presence of coliform triggers a positive coliform test. Water systems aren't allowed to have more than 5 percent of their water samples test positive for coliform each month. For a smaller water system that collects fewer than 40 samples every month, the EPA limits positive samples to one per month.

Acute MCL Violation

• An abnormal total coliform count can signal a breakdown in the water treatment process. When this occurs, the EPA requires treatment plants to test samples for fecal coliform or the presence of E.coli. A positive reading for these types of bacteria results in an Acute MCL (maximum contaminant level) violation. If this occurs, water system operators must notify the public within 24 hours after the company is notified about the violation. The company must also notify state officials by the next business day.

Monthly MCL Violation

• When more than 5 percent of sampled water contains coliform bacteria, but no fecal coliform has been found, a monthly MCL violation occurs. After notification, the EPA requires these violations to be reported to state officials by the next business day. The public must be informed within 30 days.

Coliform Removal

• To remove coliform from the water supply, suppliers disinfect the water. Treatments used include chlorine, UV (ultraviolet) light and ozone. The EPA notes that these neutralize E. Coli. If there is a violation, typical actions involve locating and removing the source of the contamination. The water supplier may also take actions to prevent future contamination, as well as repairing disinfecting equipment, according to the EPA.

Considerations

• According to the Centers for Disease Control and Prevention (CDC), one out of seven Americans use water from systems like private wells. The EPA doesn't regulate these systems. NSF international, a not-for-profit organization involved in ensuring public safety through certification and risk management, suggests that consumers test private water systems annually for total coliform levels. Consumers can request recommendations or testing from their local health departments.