Well water testing in Durham Region

Free water testing for all Durham Region residents. North Durham pick-up and drop-off: the Health Department's North Office, 181 Perry Street, Port Perry, and the Township of Uxbridge office, 51 Toronto Street (both Monday to Thursday 8:30 a.m. to 4:30 p.m., Friday 8:30 to 9 a.m.); the Township of Brock office, 1 Cameron Street East, Cannington, hands out bottles only. Regional Headquarters in Whitby (605 Rossland Road East) takes samples until 10 a.m. for same-day delivery, and the Garnet B. Rickard Recreation Complex in Bowmanville is another site. Samples must reach the lab within 24 hours.

Durham recommends testing for harmful bacteria at least three times a year.

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. If you suspect chemical contamination (pesticides, oil or gasoline), Durham says not to boil the water and to call the Durham Health Connection Line at 905-668-2020 or 1-800-841-2729.

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.