Bacteria in Drinking Water

Drinking water contaminants stemming from fecal bacteria contamination can pose a risk to human health and cause diarrhea, vomiting, stomach cramps, flu like symptoms; and diseases such as cholera, typhoid and hepatitis. While it would be expensive, and practically impossible to screen drinking water for every possible pathogen, water quality tests using coliforms as indicators of drinking water contaminants offers an inexpensive, effective, and fairly accurate method of determining the presence of disease causing organisms. 

Bacteria occur naturally in soil, vegetation and even in water. There are many different types of bacteria, some of which present no health risks, whereas others are cause for concern as they can cause health problems.

Coliform Bacteria

Coliform bacteria are found in the environment, and in the gut of warm blooded animals. They are usually harmless, and present no health risk when found in drinking water. However, as they are usually associated with animal waste products or sewage, their presence in drinking water may indicate that the water is contaminated with other pathogens that may pose a health risk.

Coliform counts give an indication of the following: total coliforms, fecal coliforms, and E. coli. Total coliforms is the broadest category, and encompasses fecal coliforms and E.coli. As total coliforms include the harmless environmental coliforms, if they are detected in drinking water there is generally no reason for alarm, except that if they managed to work their way into the water system, other drinking water contaminants may also be present. Fecal coliforms are a sub-group of coliforms that originate from animal feces or sewage. As fecal coliforms originate from fecal waste, if they are detected in drinking water, the likelihood of the water containing other drinking water contaminants and disease causing organisms is higher.

E.coli is a sub-group of fecal coliforms, which in most cases are harmless, but some strains (such as E.coli 057:H7) can harbor disease causing toxins. E.coli 057:H7 can cause severe diarrhea, stomach cramps, and vomiting, and in some cases can result in hemolytic uremic syndrome where the red blood cells are destroyed and the kidneys fail. This is a life threatening situation and requires hospitalization and treatment in an intensive care unit, often with blood transfusions and kidney dialysis necessary. Even with specialized treatment, the death rate for hemolytic uremic syndrome is 3-5%, with children, the elderly, and those that have compromised immune systems being most at risk. E.coli 057:H7 outbreaks are usually associated with eating contaminated foods, however, deaths and illness have occurred from drinking water contaminated with this strain of E.coli. While most E.coli do not pose a direct health threat to humans, the presence of E.coli in drinking water, indicates recent fecal contamination of the water source, and requires treatment by disinfection, boiling, or filtration to remove any other pathogens that may be lurking.

Legionella Bacteria

Another bacteria that occurs naturally in water is Legionella, which can cause Pontiac fever, or the more serious Legionnaires' disease, a type of pneumonia. Symptoms in both diseases include fever, chills, headaches and muscle aches, with the more severe Legionnaires' disease also affecting the lungs. According to the Centre for Disease Control and Prevention, between 8,000 – 18,000 people are hospitalized with Legionnaires' disease every year in the US alone. The number of people infected is likely to be much higher than this as many cases go unreported. While Pontiac fever typically only lasts for 2-5 days, with symptoms disappearing naturally without treatment, Legionnaires' disease is far more serious, and can be fatal in 5-30% of cases. Treatment with antibiotics is usually successful in most patients, but people with compromised immune systems are more at risk. Legionella bacteria are found naturally in water and tend to thrive in warm water conditions such as hot tubs, spas and saunas. People can become infected from breathing in steam or from drinking water that is contaminated with the bacteria.

How Does Bacteria Enter Drinking Water

Deep underground aquifers generally do not contain bacteria, as these get filtered out as the water permeates through the soil micropores. However, bacteria can readily enter an open water source through run-off from farm lands, or from sewage discharge. Bacteria can enter wells during the construction phase, and may persist if treatment is not carried out. Poorly constructed wells, or wells that are not properly sealed, can allow bacteria to enter via run-off of water contaminated with fecal matter from animal waste or sewage.

Water Purification Measures

Water purification measures to remove bacteria and other drinking water contaminants include:
  • Chlorine treatment
  • Iodine treatment
  • Boiling water
  • Treating with ultraviolet light
  • Filtration using water purification filters
In order to reduce the health risks of exposure to drinking water contaminants, it is recommended that any of the above water purification measures are undertaken to ensure that drinking water is adequately treated and safe for human consumption.


Dept of Health, Centers for Disease Control & Prevention. Patients Facts: Learn More About Legionnaires' Disease.

Dept of Heath: Centers for Disease Control & Prevention. Water-related Diseases, Contaminants, and Injuries by Type.

Michigan Dept of Environmental Quality. Coliform Bacteria & Drinking Water. Environmental Health Fact Sheet.

United States Environmental Protection Agency. Basic Information About E.coli 057:7H in Drinking Water.




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