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Coliform Bacteria in Drinking Water

Water Contaminants: Coliform Bacteria
Published on 11/4/2016

Coliform bacteria are a type of bacteria that is relatively easy to detect when grown under a certain set of laboratory conditions. Because coliform bacteria are typically present in greater numbers than disease-causing microbes and because they tend to persist in water longer, they are often used as indicators of possible contamination by harmful microbes. An absence of coliform bacteria generally indicates an absence of other microbes or pathogens.

“The presence of coliform bacteria is one of the most common water quality problems in the United States.”

The presence of coliform bacteria is one of the most common water quality problems in the United States. Because the sources of coliform bacteria are located near the ground surface, this type of contamination is more common in shallow wells than in deeper wells (>100 feet deep). However, contamination of deeper wells is possible through water flow along the well casing or other reasons.

Coliform bacteria are more likely to contaminate well water during periods of warm and wet weather. Well systems are more susceptible to contamination after heavy rainfall events or extended rainy periods.

Measurement of Coliform Bacteria in Drinking Water

Water samples for coliform bacteria must be collected in sterile bottles using specific procedures. The bacteria are then grown in a laboratory and quantified. There are three measurements of coliform bacteria:

Total coliforms. This measurement includes all coliform bacteria. These bacteria include many different species that live in different environments such as soil, water and vegetation, as well as in the intestines of warm-blooded animals. Most species of coliform bacteria are not harmful, but some coliform bacteria can cause mild or severe illness. The presence of coliform bacteria indicates a pathway for contamination of the water supply from the source of the bacteria (which could be a septic tank, sewer system, animal waste, runoff, etc.). This same pathway could potentially be taken by disease-causing organisms.

Fecal coliforms. These bacteria only include coliform bacteria that live in the intestines of warm-blooded animals, including humans. The presence of fecal coliform bacteria indicates possible contamination by human or animal waste.

coli. This is a specific species (full name Escherichia coli) of coliform bacteria. There are hundreds of different strains of E. coli, most of which are harmless to humans. However, several strains of E. coli are harmful and can result in severe illness. E. coli is specific to the intestines of humans and other organisms, so detection of E. coli indicates contamination of the water supply with human or animal waste.

Interesting fact: E. coli is often referred to as the most-studied living organism.

Health Effects Associated with Bacteria in Drinking Water

“If your water supply is contaminated with coliform bacteria, it could indicate that your system may also be contaminated with other harmful organisms, including viruses, protozoa or worms.”

Most species of coliform bacteria are harmless, but their presence can indicate the potential for contamination by other microbes. For the species of coliforms that are harmful, symptoms can include fever, abdominal cramps, and diarrhea. Children and the elderly are the most susceptible to these symptoms. Because these symptoms are similar to those of the flu and other common illnesses, it may be difficult to identify the water supply as the source of the problem without testing. Residents may become immune to bacteria present in their water supply, while visitors may become ill.

If your water supply is contaminated with coliform bacteria, it could indicate that your system may also be contaminated with other harmful organisms, including viruses, protozoa or worms. These other organisms can cause health problems such as polio, hepatitis, dysentery, vomiting and chronic diarrhea.

The U.S. Environmental Protection Agency (USEPA) requires that public water supplies monitor total coliforms. If total coliforms are detected, the systems must also be tested for E. coli. If excessive E. coli or total coliforms are found, then the water supply must take action to identify and fix the “sanitary defect” that resulted in the contamination.

It is recommended that all private water supplies be tested for total coliform bacteria each year. If total coliform bacteria are found to be present, then additional testing for fecal coliform bacteria or E. coli may be warranted. Testing for coliform bacteria is generally less expensive than testing for other pathogens, such as viruses.


How to Treat Drinking Water for Bacteria

Problems with coliform bacteria can often be fixed by taking measures to prevent surface water or insects from contaminating the water supply, such as sealing a spring box or using a sanitary well cap. Maintaining a septic system to ensure proper functioning or controlling sources of animal waste near a well or spring may also help with the problem. Shock chlorination can also be used as a one-time approach to getting rid of bacteria in the water supply once the source has been controlled.

Boiling water for one minute will safely kill all bacteria, but this is not a good long-term solution because it is energy and labor intensive and only produces a small amount of water.

If the source of bacteria to the water supply cannot be controlled, drinking water contaminated with bacteria can be treated continuously by ultraviolet (UV) light, ozonation, or chlorination.

Ultraviolet disinfection works by killing bacteria by exposing them to ultraviolet light. The light source is contained in a glass sleeve, and water is exposed to the UV light as is flows over the sleeve. This method of disinfection consumes a small but significant amount of electricity. It is important that the water be very clear so that the UV light can reach the bacteria. Anything that would make the water less than perfectly clear, such as sediment or organic matter, must be filtered out before the water enters the light chamber. The glass sleeve must also be kept clear of scale or other deposits that would block the light. Follow this link to residential whole house UV sterilizer systems.

Chlorination continuously introduces chlorine to the water through a feed system. The chlorine can take the form of a liquid or a solid. A filter should be placed before the chlorine injector to remove sediment from the water. The chlorine kills bacteria in the water, but it is consumed in the process. Chlorine is also consumed by interaction with other impurities in the water, such as iron or organic matter. Enough chlorine should be added so that there is a small amount left over after being consumed by interactions with bacteria and other impurities. Because the residual chlorine affects the taste and color of the water, it may be desirable to remove the chlorine before drinking.

Chlorination also requires a certain amount of contact time (usually 30 minutes) for it to kill the bacteria. Because of this, water is often stored in a large holding tank or run through a series of coiled pipes after being chlorinated. Chlorine systems must be maintained to ensure proper functioning, and the chlorine supply must be periodically replenished.

Ozonation is similar to chlorination in that ozone is injected into the water and kills bacteria. Ozone is a gas that is produced using electricity and then injected into the water. Ozonation systems are more costly than UV light or chlorination systems, but they can treat water for multiple contaminants, such as bacteria, iron and manganese.