What is eColi? (aka Coliform Contamination)?

What are Coliform?


In scientific terms: Coliform bacteria are readily found in soil, decaying vegetation, animal feces, and raw surface water. They are from the same family which live and reproduce in the intestines of animals.

They are not typically found in deep ground water and treated surface water.

They are indicator organisms that may be accompanied by disease-causing organisms known as pathogens. Normally, healthy individuals are not affected by their presence.

That said: individuals with compromised immune systems should be considered 'at risk'.

Coliforms are easier to detect in drinking water as they are more numerous than Pathogens. Their presence results in drinking water to be declared 'biologically contaminated'.

Excuse me .... what's a pathogen?

These are disease-causing microorganisms which include:

  • bacteria that cause cholera and typhoid fever

  • protozoa that cause dysentry

  • viruses that cause polio and hepatitis

  • helminths such as roundworm and tape worm.

    How does the laboratory detect coliforms in a water sample?

    Uh-Oh....Did you know examining water under a microscope is not reliable in finding them?

    Colilert presence/absence detection method


    Briefly, two separate examinations are combined.

    First, the 100 mL sample is combined with growth medium, and then incubated for 24 hours at 35.0 degrees Centigrade.

    After 24 hours, only coliform bacteria will use the growth medium for food, resulting in a change in the water sample's appearance.

    At the same time, a second examination is performed to determine if the coliform present is from feces. Thus, the test is completed 24 hours after it has begun.

    A TOTAL COLIFORM ABSENT report means that there are no coliform bacteria present at the time of sampling and the water may be considered bacteriologically safe to drink.

    A FECAL COLIFORM (E.COLI) PRESENT report means that fecal coliform bacteria is present at the time of sampling and the water may not be considered safe to drink. Typically, you will be advised to super-chlorinate and/or make modifications to the water system.


    The California Department of Health Services sets drinking water standards and has determined that the presence of any coliform bacteria in drinking water is a possible health concern.

    Criteria: A 100 milliliter sample of water must be absent of coliform bacteria to be considered safe to drink.

    How did the water become contaminated?

    Some degree of contamination almost always are found in surface waters, such as streams, creeks, and lakes because of exposure to animals, humans, aquatic life, etc.

    General Rule:

    Always treat raw surface waters prior to domestic use. This includes disinfection and filtration to remove turbidity and parasites that are resistant to simple disinfection. Ultra-Violet light will disinfect while a 2-Micron filter will trap particles and E.Coli.

    In Rural Areas:

    Wells and springs can become contaminated by:

  • faulty construction,

  • poor protection from rain, flooding or other surface activity,

  • a shallow water table,

  • entrance of unfiltered surface water via rock fractures,

  • close proximity to a sewage disposal system or leaky sewer pipe,

  • and/or contamination during repair or reconstruction.

    A false, positive coliform count can occur by contaminating the water sample (e.g., putting one's finger into the water sample bottle) or by using a non-approved water sample bottle.

    A well or spring should be super-chlorinated prior to the coliform test, especially if a repair has been made and the system was not chlorinated at the time.

    How do I cure my contamination problem?

    Great question!

    It is important to determine the source of the problem by carefully examining:

  • the well

  • the storage tank

  • the spring etc...

    Where the well/spring is properly constructed, spot chlorination may suffice.

    Here's How:

  • Pour chlorine bleach down the well shaft (or into the spring containment box)

  • Let it stand for 30-minutes,


  • Open each tap individually. This will bring the chlorine solution into contact with the entire water system.

  • When you notice the chlorine odour, shut off the tap and do the same for the next one etc...

    Do not operate the water system for 12-hours (or over-night)

    The next day, open taps and the running water will flush out the chlorine odour. A swimming pool test kit can be used to check if chlorine is still present.

    Important: Re-test for coliform contamination. Note: Where coliform contamination cannot be eliminated, the well/spring may require to be re-built.

    I Get it! now....How much chlorine do we use to 'spot' disinfect?

    Great question!

    Use household bleach which is 5.25% chlorine.

    A 6-inch diameter well will yield 100-gallons of water per 66-ft.

    Use 1 quart of bleach for every 66-feet of water.


    Wrapping it all up.....

    Unless you have found and corrected the cause of the contamination, your water supply will have recurring bacteria problems.

    Sometimes the problem may be the ground water itself.

    A possible remedy is to install a continuous disinfection system. Elsewhere on this site we discuss possible options and provide a way to get your specific questions answered.

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