Cadmium in well water: limits and sources
The limit for cadmium is 0.005 mg/L (5 µg/L) in both the US and Ontario. Most well results come back below detection. Long term exposure above the limit can damage the kidneys.
- US (EPA)
- 0.005 mg/L.
- Ontario
- 0.005 mg/L.
What it is
Cadmium can come from corroding galvanized pipes, from some fertilizers, or from industrial waste and old landfills. It is rarely found naturally at high levels.
What your number means
- Within limitsBelow 0.0025 mg/L
Under the limit by a comfortable margin.
- Close to limit0.0025 to 0.005 mg/L
Under the limit but more than halfway there. Retest within a year.
- Above limitAbove 0.005 mg/L
Use another source for drinking and cooking, contact your health department and retest to confirm.
What to do
- If you have old galvanized plumbing, run the tap before drinking and consider replacing it.
- Above the limit, use another source for drinking and contact your health department.
- Reverse osmosis removes cadmium.
How often to test
With a full panel every 3 to 5 years.
Common questions
Where does cadmium in tap water come from?
In homes it most often comes from corroding galvanized pipes, especially with acidic water. In groundwater it usually points to industrial or landfill sources.
Does a carbon filter remove cadmium?
Most basic carbon filters do not. Look for reverse osmosis or a filter certified to reduce cadmium.
Sources: EPA drinking water regulations; Ontario Drinking Water Quality Standards (O. Reg. 169/03). Limits checked November 2026.