Well water testing in Dufferin County

Public Health Ontario tests well water for bacteria (E. coli and total coliforms). Pick up a bottle at a public health office or a participating municipal office. Samples go back to the Guelph (160 Chancellors Way), Fergus (490 Charles Allen Way) or Orangeville (180 Broadway) offices Monday to Thursday, 8:30 a.m. to 4:30 p.m., with short Friday-morning windows; to the Mel Lloyd Centre in Shelburne (Monday and Wednesday mornings); to reception at Palmerston District Hospital or Louise Marshall Hospital in Mount Forest; or to the Township of Erin office in Hillsburgh (Monday mornings).

Test for bacteria at least three times a year; spring is the most important time. Add a cell number to the requisition form to get text alerts about contamination.

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. For nitrates, sodium, fluoride, metals or other chemicals, contact a private laboratory.

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.