Well water testing in Grey County

Free bacteria testing for private drinking-water systems, run by Public Health Ontario. Kits are picked up and samples dropped off at 14 Grey-Bruce locations, including Owen Sound and Walkerton; a Public Health Ontario courier collects Grey County samples on Thursdays.

Grey Bruce Public Health recommends testing at least three times a year, after any work on your well or water system and after significant weather events.

Public Health Ontario's lab tests only for indicator bacteria: total coliforms and E. coli. Samples have to reach the lab within a day or two, so collect them early in the week and check the drop-off cut-off times. Chemicals, metals and minerals need a private lab; nitrate testing is recommended, especially if an infant will drink the water.

Ontario's guide to testing and treating private wells reads the counts (per 100 mL) like this:

• E. coli above 0: unsafe to drink, with evidence of animal or human waste getting into the well. Stop drinking the water and call the health unit right away.
• Total coliforms above 5, no E. coli: significant evidence of bacterial contamination, usually surface water getting in. The water may be unsafe to drink: call the health unit, inspect and repair the well, shock-chlorinate it if needed and retest.
• Total coliforms of 5 or fewer, no E. coli: some evidence of bacteria, which may not be significant at these low levels. Keep testing to track the pattern.

Boiling water at a rolling boil for at least one minute kills harmful organisms but doesn't remove dissolved contaminants. To disinfect, the province says to shock-chlorinate the well and the entire household plumbing system. Between tests, check that the well cap and the sealant around the casing aren't cracked or damaged, and keep the ground sloping away from the well: Ontario's Wells Regulation requires owners to maintain a well so surface water can't get in.

Ontario's auditor general estimated in 2025 that about 1.3 million Ontarians rely on private wells, and that fewer than a third of well owners had tested in the previous 12 months (as reported by CBC). Well water can change with the seasons, after heavy rain or snowmelt, and after work on the well, which is why the health units ask for several tests a year.

• Bacteria (total coliforms and E. coli), several times a year and after flooding, heavy rain or work on the well.
• Nitrate, especially near farmland or septic systems: the province flags nitrate above 10 ppm as a health risk for infants, and reverse osmosis or distillation treats it.
• Naturally occurring minerals such as arsenic, uranium and radium, which the province lists as long-term health risks; a private accredited lab tests for them.

Read more: The well water guide.