Radium in well water: the 5 pCi/L limit
The EPA limit is 5 pCi/L for radium 226 and radium 228 combined. Long term exposure above the limit raises the risk of bone cancer. A water softener or reverse osmosis removes it.
- US (EPA)
- 5 pCi/L, radium 226 and 228 combined.
- Ontario
- Sets limits for each isotope in Bq/L. Ask your public health unit.
What it is
Radium occurs naturally in some bedrock, especially sandstone aquifers in parts of the Midwest and some granite areas. Labs often report radium 226 and 228 separately, so add them together to compare with the limit.
What your number means
- Within limitsBelow 2.5 pCi/L
Under the limit by a comfortable margin.
- Close to limit2.5 to 5 pCi/L
Under the limit but more than halfway there. Retest within a year.
- Above limitAbove 5 pCi/L
Use another source for drinking and cooking, contact your health department and retest to confirm.
What to do
- If your lab reported radium 226 and 228 separately, add them together.
- Above the limit, a water softener (cation exchange) or reverse osmosis removes radium.
- Ask about gross alpha and uranium tests too.
How often to test
Once, and again every few years if your area has known radium in groundwater.
Common questions
Does my water softener remove radium?
Yes. A standard cation exchange softener removes radium along with hardness, as long as it is maintained.
Is radium the same as radon?
No. Radium is a radioactive metal dissolved in water. Radon is a gas that forms when radium decays.
Sources: EPA radionuclides rule; EPA drinking water regulations. Limits checked November 2026.