Drinking water contaminated with coliform bacteria is concerning because these organisms serve as a warning sign of potential health risks. Coliforms are a broad group of bacteria found widely in the environment. Their presence in a water supply indicates a breakdown in the system’s integrity, suggesting a pathway exists for more dangerous disease-causing organisms (pathogens) to enter. Safe drinking water standards require the complete absence of coliform bacteria, meaning any positive test result signals contamination. Health effects range from no illness to severe complications, depending on the specific pathogens present alongside the coliforms.
Defining Coliform Bacteria
Coliform bacteria are a diverse family of microorganisms existing naturally in soil, on vegetation, and in the digestive tracts and feces of warm-blooded animals. Most coliforms are generally harmless, but they are used as “indicator organisms” in water quality testing because they are easily detected. Their presence suggests that conditions are suitable for pathogens (viruses, parasites, or harmful bacteria) to survive, which are often harder to test for directly.
A positive test for total coliforms indicates a general breach in the water system, such as a cracked well casing. If a sample tests positive for total coliforms, it is followed up with a test for Escherichia coli (E. coli). The presence of E. coli is a more specific and serious finding, strongly indicating contamination by human or animal waste. This fecal contamination suggests a higher probability that other harmful microorganisms—like Salmonella, Giardia, or norovirus—are also present.
Common Symptoms of Exposure
Ingesting water contaminated with non-pathogenic coliforms or associated bacteria typically results in a self-limiting gastrointestinal illness. Symptoms usually begin two to five days after exposure, though the incubation period varies. Common symptoms include diarrhea, abdominal cramps, and nausea.
Individuals might also experience flu-like symptoms, such as a low-grade fever, fatigue, and occasional vomiting. These illnesses are generally mild and resolve within a few days to a week. The severity depends on the individual’s age and health status; children, the elderly, and those with weakened immune systems are more susceptible to severe illness.
The Specific Danger of Pathogenic E. coli
While most coliforms cause mild illness, the danger rises significantly if the contamination includes pathogenic strains of E. coli, particularly Shiga toxin-producing E. coli (STEC), such as E. coli O157:H7. This strain produces potent toxins that damage the intestinal wall, leading to a severe illness. Initial symptoms of a pathogenic E. coli infection include intense abdominal pain and severe, often bloody, diarrhea.
A serious complication of STEC infection is Hemolytic Uremic Syndrome (HUS), which develops in 5% to 10% of cases, typically a week after diarrhea begins. HUS destroys red blood cells and causes kidney failure due to Shiga toxin damage. This complication is dangerous for young children and older adults, often requiring intensive medical treatment, including dialysis. Even after recovery, some HUS patients may have long-term abnormal kidney function or face complications like high blood pressure.
Immediate Actions After Suspected Contamination
If you suspect your drinking water is contaminated or a test result is positive for coliform bacteria, immediately stop using the water for consumption. This includes drinking, cooking, washing produce, brushing teeth, and making ice until the water is confirmed safe. Use bottled water, or boil all water intended for use at a rapid, rolling boil for at least one minute to kill potential pathogens.
Immediately contact your local health department or water utility provider to report the issue and seek guidance on testing and remediation. If household members experience severe or bloody diarrhea, persistent vomiting, or signs of dehydration, seek medical attention. Private well owners typically require professional testing and shock chlorination—adding a high concentration of chlorine—to disinfect the entire system.