8 Things you Need to Know About your Bacteria in Water Analytical Results

Posted on December 22, 2020

CARO Bacteria Water

If you have come this far, you already know that your well water should be free of bacteria, viruses and parasites and that it is a good idea (and advised by Health Canada!) to get your well water tested by a qualified laboratory on a routine basis. Following is a summary of the most frequent questions we get about when and how to test your water, as well as how to understand your report once your results are in.

To keep things simple, we will focus specifically on E. coli and Coliforms, as defined in Table 1 of the Guidelines for Canadian Drinking Water Quality, as issued by Health Canada. If you are looking for guidance on different bacteria or microorganism (we test for a lot of different critters!), please scan the information below and contact us at [email protected] if you do not find what you are looking for.

1. How often do I have to test my well water?

Health Canada recommends that private well water is tested for bacteria, including E. coli and total Coliforms, every six (6) months. In addition to routine monitoring for bacterial parameters (which can indicate whether or not your water is safe to drink), creating a schedule to test the overall quality of your water on an annual or bi-annual basis will help to ensure that your water, from source to tap, is safe to drink. Here at CARO, we offer a variety of drinking water test packages through our online store, the most popular of which is the Essential Drinking Water Package, for a detailed assessment of your water chemistry.

2. What bacteria are required to be tested in my well water, and how do I know what is considered “safe”?

Testing for all known pathogens can be a lengthy and expensive process. The Guidelines for Canadian Drinking Water have defined Maximum Acceptable Concentrations (MACs) for two of the most common indicator bacteria: E. coli and Total Coliforms. Not only potentially harmful on their own, but these bacteria may also signal that your water has become contaminated by other microorganisms.

Escherichia coli (E. coli) comes from human and animal feces, and the presence of E. coli in your drinking water means that your water may cause unwanted health effects (it is not safe to drink). According to the Canadian Drinking Water Quality Guidelines, the maximum acceptable concentration (MAC) of E. coli is NONE per 100ml sample of water.

Total Coliforms are found naturally occurring in soil, water, on vegetation, and in feces (human and animal); the maximum acceptable concentration (MAC) of total Coliforms is NONE per 100ml sample of water. Unlike E. coli, the presence of total Coliforms does not necessarily mean that your water is unsafe to drink. A positive result here indicates that your water source is vulnerable to microorganism growth and that you should investigate further with additional or more frequent monitoring.

3. What should I do if my results show possible contamination?

We recommend that you resample your well water as soon as possible to confirm the initial result. If your initial report shows a positive E. coli count, you may want to consider boiling your water until confirmatory testing has been completed. If the second report confirms that your drinking water exceeds the Guideline value, contact your local Health Authority’s Drinking Water Officer (DWO) for advice on how to proceed. We also suggest that you start investigating the source of potential contamination and begin planning a long-term treatment solution for your water.

4. How do I Read my Report?

When you receive your test results from CARO, the second column (Result) tells you if your sample falls above or below the maximum acceptable concentration (MAC), which is shown in the adjacent column, labelled “Guideline.” In cases where your sample EXCEEDS the guideline value, your results will be highlighted in red (see images below).

A note from your Scientist: The column “RL”, next to the Guideline Value, stands for “Reporting Limit.” This is the lowest number detectable by the lab; it is NOT your result. You may have also noticed that your result reads “<1” and not “0”: that is because we cannot see 0 bacterial cultures, but we can see 1!

Acceptable Levels: Total Coliforms and E. coli <1 CFU/100 mL

CARO Water Test Result

Not-Acceptable Levels: Total Coliforms or E. coli >1 CFU/100 mL

CARO Water Test Result

5. Are there other formats available to present my results?

When well water is tested for bacteria (and is safe to drink), the results may appear using any of the following terminologies. When it comes to Total Coliforms and E. coli in relation to the Canadian Drinking Water Guidelines, these terms all mean the same thing – your water is safe to drink!

  • Absent
  • 0 colony-forming unit per 100 millilitres (0 CFU/100 mL)
  • Less than 1 colony forming unit per 100 millilitres (< 1 CFU/100ml)
  • Non-detected (ND)

6. What are “Background Colonies”? I did not ask to test for these!

Every time CARO runs a drinking water sample for Total Coliforms and E. coli, we also examine the incubated sample for “Background Colonies.” These are all the other bacteria (i.e., not Total Coliforms or E. coli) that have also grown on the testing media. Although we do not identify every unique bacterium by name, their presence is useful in identifying situations where drinking water may be at risk for future contamination issues – so we keep an eye out for you!

When the Background Colony count is low, we do not report this data. If, however, the analyst notes that the Background Colony count is high (I.e., it exceeds 200 CFU/100mL), we will include this information on your report as a precautionary note. This is an indication that the water system should be flushed or inspected, as it is a favorable environment for bacterial growth. Consider this data an add-on with purchase. ?

7. What does “Overgrown” mean in my report?

The term “overgrown,” also known as confluent growth, refers to bacterial growth covering the surface of the membrane filter or culture media such that colonies are not discrete and therefore cannot be quantified (i.e., there are too many to count reliably.) Overgrowth can be caused by the presence of excessive concentrations of bacteria, but it can also be the result of bacterial growth patterns and/or colony morphology. Depending on the bacterial parameter being tested (see Question 2, above), overgrowth may indicate an immediate health risk or the need for additional testing.

8. What does the alphanumeric code, “HT3” Mean?

This term, listed under the “Qualifier” column, tells you that the microbiological analysis was initiated outside the maximum recommended holding time of 30 hours. This is the time that has been cited by Health Canada as the maximum amount of time that should elapse between sample collection and analysis. Outside this time, there is scientific evidence to suggest analytical results may no longer be representative of site conditions. These hold times are often short, and difficult to hit if you are taking your sample from a remote property. If you see this qualifier on your report, you may want to consider resampling, and finding a quicker option for returning your sample to the lab.

We hope this post has helped you understand more about the quality of your drinking water. For further information, please refer to the Guidelines for Water Quality provided by Health Canada here. If you still have questions about your results, please Contact Us and we would be happy to help.

Thank you for helping to make the world safer and healthier – one drinking water sample at a time!


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