Coliform bacteria are a group of microbiological contaminants regulated as part of the Safe Drinking Water Act (SDWA) by the US Environmental Protection Agency (USEPA). Total Coliforms are usually not pathogenic, however, their presence in drinking water indicates the potential presence of other disease causing pathogens. The presence of E. coli bacteria in drinking water indicates that an urgent public health problem may exist.
The Total Coliform Rule is based on the presence or absence of coliform bacteria in a given sample. All samples testing positive for the total coliform group must be followed by repeat sampling and testing to determine the presence of any fecal coliforms.
The total number of monthly samples required for compliance purposes is based on population served. The minimum number of samples per month for Providence Water is 150 per month. On average, the Providence Water laboratory collects and tests approximately 200 samples per month for coliform bacteria.
The maximum contaminant level for total coliforms is stated in terms of a percentage of positive results per month. Specifically, to be in compliance:
- no more than 5.0 percent of the monthly samples can test positive if 40 or more samples are analyzed each month
Water systems can be in violation of the monthly MCL for total coliforms in two ways:
- if the number of total coliform positive samples exceeds 5.0 percent of the monthly samples when 40 or more samples are analyzed; or
- if there is a combination of:
- a coliform positive original sample that is also positive for fecal coliform followed by a positive coliform repeat sample; or
- a coliform positive original sample followed by a coliform positive repeat sample that is also positive for fecal coliform or E.coli