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State Water Resources Control Board Division of Water Quality GAMA Program GROUNDWATER INFORMATION SHEET Bacteria Indicators The purpose of this groundwater information sheet is to provide general information regarding a specific constituent of concern (COC). The information provided herein relates to wells (groundwater sources) used for public drinking water, not water served at the tap. GENERAL INFORMATION Constituent of Total coliforms, fecal coliforms and Escherichia coli(E. coli) Concern Aliases None Chemical None Formula CAS No. N/A Summary Coliforms, a group of common bacteria, are generally harmless to humans. However, some coliforms may cause illness in humans, and the presence of coliforms at any concentration is an indication that other harmful micro-organisms may be present. Fecal coliforms such as E. coli, and other types of harmful bacteria are found in animal and human wastes, and when detected they are indicators of water supply contamination. Ingestion of water containing coliform bacteria increases the risk of contracting a water-borne illness. In 1989, (revised in 2013), the United States Environmental Protection Agency (US EPA) established the Total Coliform Rule (TCR) to help reduce pathogens in public drinking water. The TCR established a maximum contaminant level (MCL) based on the presence or absence of total coliforms in public water systems, and required public water systems conduct sanitary surveys. The US EPA published the Ground Water Rule (GWR) in 2006, which required groundwater systems that are at risk of fecal contamination to take corrective action to reduce cases of illness and deaths due to microbial pathogens exposure. This rule does not address private (domestic) wells since they are not subject to US EPA regulation. Domestic well owners are individually responsible for testing and maintaining their water supply. Revised September, 2019