E. coli (Escherichia coli) in Drinking Water

E. coli (Escherichia coli) is a type of bacteria commonly found in the intestines of humans and warm-blooded animals. While most strains are harmless, certain pathogenic strains -- particularly E. coli O157:H7 -- can cause severe and potentially life-threatening illness. The presence of E. coli in drinking water is one of the strongest indicators of fecal contamination, meaning that human or animal waste has entered the water supply. This is considered a public health emergency because where E. coli is found, other dangerous pathogens like Giardia, Cryptosporidium, and viruses are likely present as well.

Infection from pathogenic E. coli in water can cause severe bloody diarrhea, abdominal cramps, nausea, and vomiting. In serious cases -- particularly in young children and the elderly -- it can progress to hemolytic uremic syndrome (HUS), which causes kidney failure and can be fatal. Even non-pathogenic E. coli strains in drinking water signal a serious treatment failure or distribution system breach that demands immediate action.

E. coli contamination events are most common after heavy rainfall or flooding, which can overwhelm sewage systems and wash animal waste into water sources. Well water is particularly vulnerable, especially shallow wells located near septic systems, livestock operations, or areas prone to flooding. Public water systems are required to maintain disinfection residuals that prevent E. coli survival, so detections typically indicate a breakdown in the treatment or distribution system. If E. coli is detected, a boil-water advisory is usually issued immediately.