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Water Education: Health-unit water testing

January 17, 2019  By Jeff Wahl

Bacterial water contamination is a serious issue that has ramifications for human health. The importance of a health-unit water test cannot be overstated as it can identify potential for illness due to bacteria present in water.

When submitting a water sample to a public health unit in the province of Ontario, do you know what is being tested for? Do you assume that the safety of the water is being tested for and the results are a good determination of overall drinking water quality? Does a good test result put your mind at ease that the water is safe for consumption for your customers?

E. coli and total coliforms are the only two parameters tested for in a health-unit water sample and they can cause illness, with severe cases resulting in fatalities. The Canadian Drinking Water Guidelines (CDWG) contain 104 parameters with minimum safety levels of which E. coli and total coliform are only two of those parameters. The remaining 102 parameters are not part of a health-unit water test. Municipalities are required to test and maintain drinking water standards. This process identifies the presence of contaminants as it involves daily routine monitoring and reporting. What happens when you step out of the city limits and venture into the country? There is no standard regulation for private facilities and owners are left on their own for monitoring water quality. The health-unit test is free for all private residence owners and is often mistaken by the public to be like or the same as municipal testing.


Experience has shown that when many people receive good test results, they believe the water is safe to drink and then forget about it until next year when they may or may not sample again. A calendar year has changing weather patterns, temperature and movement of water. It is important to remember that a health-unit sample is a picture of one day in the year. What changes in the other 364 might affect the quality of the water in a well?

Rural Ontario, for example, is a vast area with varying topography and water quality. Contaminants such as total dissolved solids (TDS), water hardness, sulphates, chlorides, manganese, phosphorus, herbicides, pesticides, petroleum products and many others can be present in levels that can exceed the CDWG guidelines. One example of this; safe TDS levels are less than 500 ppm with greater than 1,000 ppm and above not recommended for consumption.

Clear and virtually invisible in water, TDS is not a requirement for testing at the health unit. Water testing by an accredited laboratory in the Manitoulin Island area has identified levels exceeding 10,000 ppm with ranges from 1,000 ppm to 3,000 ppm being common. All these tests have passed the health-unit test as they contained no E. coli or coliform but failed the Canadian Drinking Water Guidelines.

As part of the well drilling process a water sample is often submitted. Consider what else might be in the water and be sure to inform the customer of the bacterial-only nature of the test. It is good practice to provide this information to your customer as what you see flowing from the well may be clean, clear, without any smell, but not safe water for drinking.

A health-unit water test is not a statement of the overall drinking water quality. The next time you recommend a sample be taken to a health unit remember that it is a bacterial test and not a complete analysis of overall water safety or drinkability. Have the customer consult a qualified water treatment professional for advice on additional water testing options.

Jeff Wahl has 20 years of experience in the water treatment industry. He is the chief executive officer of Wahl Water and a water educator. For more information, contact Jeff at

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