Chromium in well water: total chromium and hexavalent
The EPA limit for total chromium is 0.1 mg/L and the Ontario standard is 0.05 mg/L. Most wells are far below. Total chromium includes hexavalent chromium, the more toxic form.
- US (EPA)
- 0.1 mg/L total chromium.
- Ontario
- 0.05 mg/L total chromium.
What it is
Chromium occurs naturally in some rock and soil, and can come from industrial sources such as plating, tanning and wood treatment. Labs usually report total chromium. A separate test can measure hexavalent chromium.
What your number means
- Within limitsBelow 0.05 mg/L
Under both the US and Ontario limits.
- Worth a look0.05 to 0.1 mg/L
Above the Ontario standard, under the EPA limit. Retest, and ask about a hexavalent chromium test.
- Above limitAbove 0.1 mg/L
Above the EPA limit. Use another source for drinking and contact your health department.
What to do
- If total chromium is detected, ask your lab about testing for hexavalent chromium.
- Reverse osmosis removes both forms.
- If you live near industry that used chromium, tell your health department.
How often to test
With a full panel every 3 to 5 years.
Common questions
What is hexavalent chromium?
It is the more toxic form of chromium, known from industrial contamination. The total chromium test includes it, so a low total result means hexavalent chromium is low too.
Is chromium a nutrient?
Trivalent chromium is a trace nutrient in food, but the drinking water limits still apply to total chromium.
Sources: EPA drinking water regulations; Ontario Drinking Water Quality Standards (O. Reg. 169/03). Limits checked November 2026.