Well water testing in York Region

Free bacteria testing for owners of private drinking-water wells, analyzed by Public Health Ontario for total coliforms and E. coli. Pick up bottles weekdays from 8:30 a.m. to 4:30 p.m. and drop samples off Monday to Thursday before each site's cut-off: in Georgina at 20849 Dalton Road, Sutton (10 a.m.), 24262 Woodbine Avenue, Keswick (11 a.m.) and the Georgina Civic Centre, 26557 Civic Centre Road (10 a.m.); in Newmarket at 17150 Yonge Street (10 a.m.); in Richmond Hill at 50 High Tech Road (11 a.m.); in Vaughan at 9060 Jane Street (11 a.m.); and in Unionville at 4261 Highway 7 (11 a.m.). The Public Health Ontario lab at 81 Resources Road in Etobicoke takes drop-offs only, weekdays 8 a.m. to 2 p.m.

Once results are safe, York Region recommends testing each spring, summer and fall, and again after well construction and disinfection, after the well has sat unused for a long time, after snowmelt and after heavy rain or flooding.

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. The lab no longer tests well water for nitrates or sodium; York Region suggests a private licensed lab at your own expense, and notes that boiling kills bacteria but concentrates chemicals.

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.