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How to test your well water for coliform bacteria - the invisible danger

Posted by James Layton on
How to test your well water for coliform bacteria - the invisible danger
Safety standards for drinking water

The U.S. Environmental Protection Agency (EPA) requires municipal water treatment operators to monitor coliform bacteria levels in the water, with the health standard being zero total coliform. However, private wells are not monitored by federal, state, or local authorities—the responsibility for well water safety lies in the homeowner’s hands. Testing your home’s well water for bacteria is the only reliable way to know if your water is safe, as most of the time you cannot tell by the look, taste, or smell of the water if it contains disease-causing organisms (pathogens).

What are coliform bacteria?

coliform bacteria in well water

Total coliform bacteria are found in the environment and feces of all warm-blooded animals, including humans. There are many types of coliform bacteria and while most don’t cause illness, their presence in your well water indicates that there could be harmful pathogens in your water supply.

There are three groups of coliform bacteria:

  1. Total coliform—a large collection of different kinds of bacteria. 
  2. Fecal coliform bacteria—a subgroup of total coliform bacteria.
  3. E. coli—a subgroup of fecal coliform.
Potential health effects

Water pollution caused by fecal contamination is a serious problem, due to the potential for contracting diseases from pathogens, such as some strain of E. coli. They can cause severe illness, with symptoms including severe diarrhea and abdominal cramps. Children, the elderly, and people with compromised immune systems are the most susceptible.                   

How do coliform bacteria get into well water?

Coliform bacteria are called "indicator organisms" because their presence indicates a possibility of disease-causing bacteria, such as E. coli, being in the water. A positive coliform bacteria test does not necessarily mean your drinking water is unsafe, but it does mean that something is wrong. 

Common sources of coliform contamination of wells

So, how can you spot if coliform bacteria may have contaminated your well water? Look out for the following signs:

  • A loose, missing, or defective well cap—seals around wires, pipes, and where the cap meets the casing may be cracked, letting in contaminants.
  • Contaminant seepage through the well casing—cracks or holes in the well casing allow water unfiltered by soil to enter the well. This seepage is common in wells made of concrete, clay tile, or brick.
  • Contaminants seeping along the outside of the well casing—many older wells were not sealed with grout when they were constructed. If the area around the well casing is flooded, it can force bacteria into the well. 
  • Well flooding—a common problem for wellheads located below the ground in frost pits that frequently flood during wet weather.
  • Standing water next to the well—make sure that runoff water does not pool near your well.
  • Recent work on the well, pump, or plumbing system. 
  • Animal waste entering the water supply or malfunctioning septic systems.
  • Contamination of the water supply from pump replacement, drilling, and well repairs.
Testing your well water for coliform bacteria

coliform bacteria in water - negative and positive result

The best way to determine whether harmful pathogens are present in your well water is by testing for total coliform. Their presence or absence gives a general indication of the sanitary condition of your water supply.

The Health Metric Bacteria Test makes it easy to check your water supply for coliform contamination. The at-home test uses a EPA-approved method for screening well water for the presence of coliform bacteria. Simply fill the jar with water and wait 48 hours. If the water in the jar turns yellow, the test is positive for coliform bacteria. If it remains purple, the results are negative. More information on using the Health Metric bacteria test kit along with helpful testing tips can be found here.

What to do if the test is positive

The Health Metric bacteria test is a “presumptive” test, providing a simple a yes/no result. A positive indicates that your water supply is being contaminated somewhere in the well or plumbing system, so repairs or modifications may be required. In some cases, the source of contamination can only be controlled by an in-home treatment system. A water treatment professional may suggest a chlorine injection or UV disinfection system. 

Boiling the water is advised until disinfection and retesting confirms that contamination has been eliminated. If necessary, your water can be tested by a lab to specifically check for the presence of harmful coliform strains. 

Test your well at least once a year

The EPA and local water authorities recommend testing your well for bacteria at least once a year. If you’ve had maintenance or repairs made to your well, test to make sure the well has not been accidentally contaminated. 

You should also test if:

  • There are known problems with well water in your area.
  • You have experienced problems near your well, such as flooding and land disturbances.
  • You notice a change in water quality such as taste, color, or odor.
  • Whenever the well is inundated by flood waters or surface runoff.

For more information on how to test for a safe well water supply, contact us on

Well Water Test Kit—simple and professional testing with no hidden feeswell water text kit Health Metric

The Health Metric Well Water Test Kit includes a coliform bacteria test plus seven other important water quality parameters to determine the quality of your water. The test kit allows you to test your well water and compare the results to official EPA standards. Find out more.

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