Fecal coliforms are a subset of coliform bacteria that are associated with the fecal matter of warm-blooded animals. Their presence in water indicates potential contamination by sewage or animal waste.
Fecal coliforms are bacteria that can grow at elevated temperatures (44.5 degrees Celsius) and are used as indicators of fecal contamination in water quality testing. The most well-known member of this group is Escherichia coli (E. coli), which is the most reliable indicator of recent fecal contamination because it is found almost exclusively in the intestines of humans and other warm-blooded animals. Fecal coliform testing is a standard requirement for assessing the safety of drinking water sources, recreational waters, and shellfish harvesting areas. The EPA's recreational water quality criteria recommend that E. coli levels not exceed a geometric mean of 126 colony-forming units (CFU) per 100 mL for freshwater. Sources of fecal contamination include failing septic systems, combined sewer overflows, agricultural runoff from livestock operations, and wildlife. Elevated fecal coliform counts in shellfish growing waters can trigger closures to protect public health from waterborne diseases such as gastroenteritis, hepatitis, and cholera.