Escherichia coli, or E. coli, is a large and diverse group of bacteria found in the environment and the lower intestines of people and warm-blooded animals. While most strains of E. coli are harmless and part of a healthy intestinal tract, certain strains can cause illness. This can range from mild intestinal distress to severe complications. The presence of any E. coli in water is a public health concern, as it indicates contamination of the water supply.
Sources of Water Contamination
E. coli finds its way into water systems almost exclusively through fecal contamination. Because the bacteria live in the intestines of humans and animals, its presence in water is a direct indicator that waste has entered the supply. Agricultural runoff is a significant source, as rainfall can wash animal manure from farms and feedlots into nearby streams, rivers, and groundwater.
Another major contributor is human sewage. Overflows from wastewater treatment systems, especially during heavy rain, can release untreated or inadequately treated sewage into the environment. Failing septic systems can leach waste into the surrounding soil and groundwater, while wildlife also contributes waste from animals living near water sources. These contamination events are often worsened by heavy precipitation.
Health Implications of Contaminated Water
Ingesting water contaminated with pathogenic E. coli can lead to a range of health issues. Harmful strains like Shiga toxin-producing E. coli (STEC) can cause serious illness. The most well-known STEC strain, E. coli O157:H7, produces a powerful toxin that can damage the lining of the small intestine, leading to the common symptoms of an infection.
Symptoms typically develop within two to four days of exposure and include severe stomach cramps, diarrhea that may become bloody, and vomiting. While many people recover within a week, some individuals are at a higher risk for severe complications. Young children, the elderly, and people with compromised immune systems are particularly vulnerable.
In these susceptible groups, an E. coli infection can progress to a life-threatening condition called hemolytic uremic syndrome (HUS). HUS develops in about 2-7% of infections and is characterized by the destruction of red blood cells and kidney failure. It is a leading cause of acute kidney failure in children and requires intensive medical care, often including blood transfusions and kidney dialysis.
Identifying E. coli in Water Supplies
The detection of E. coli in water is important because it acts as an “indicator organism.” Its presence signals that the water has been contaminated with fecal matter and could also contain other dangerous waterborne pathogens like Cryptosporidium, Giardia, and norovirus. Because testing for every possible pathogen is complex and expensive, water systems test for E. coli as a reliable way to gauge water safety.
Public water systems are mandated by regulations like the U.S. Environmental Protection Agency’s Safe Drinking Water Act to regularly test their water. If contamination is found, the utility must notify the public and take corrective action. For individuals who rely on private wells, the responsibility for testing falls on the homeowner. Well owners should have their water tested annually for bacteria by a state-certified laboratory, and also after a flood, a septic system malfunction, or if there are noticeable changes in the water’s taste, smell, or appearance.
Water Treatment and Disinfection
When E. coli is detected in a water supply, immediate action is necessary. The most common short-term solution is a boil water advisory. Bringing water to a rolling boil for at least one minute effectively kills E. coli and other harmful microorganisms, making it safe for drinking, cooking, and brushing teeth.
For a long-term solution to recurring contamination, several water treatment technologies are effective. Chlorination is a widely used method where chlorine is injected into the water system to kill bacteria. Another highly effective approach is ultraviolet (UV) light disinfection, where water is exposed to UV rays that destroy the genetic material of microorganisms, rendering them harmless. Other treatment options include ozonation and specific types of filtration like reverse osmosis. The choice of treatment depends on the water source and contamination level, and a combination of methods may be recommended for private wells.