Gross alpha in well water: what the test means
The EPA limit for gross alpha is 15 pCi/L, not counting radon and uranium. It is a screening test: a high result means you should test for uranium and radium to find the source.
- US (EPA)
- 15 pCi/L.
- Ontario
- Uses screening levels. Ask your public health unit about follow up tests.
What it is
Gross alpha measures the total alpha radiation from natural radioactive elements in your water, mostly uranium and radium from bedrock. It doesn't say which element is responsible.
What your number means
- Within limitsBelow 7.5 pCi/L
Comfortably under the EPA limit.
- Close to limit7.5 to 15 pCi/L
Under the limit. Ask about testing for uranium and radium.
- Above limitAbove 15 pCi/L
Test for uranium and radium, use another source for drinking until you know the cause, and ask about treatment.
What to do
- Ask your lab to test for uranium and combined radium 226 and 228.
- Treatment depends on the source: reverse osmosis covers both, a water softener (cation exchange) removes radium, and anion exchange removes uranium.
- Test for radon too, since the same bedrock often produces all three.
How often to test
Once, and again every few years if your area has known radioactivity in groundwater.
Common questions
Does gross alpha include radon?
No. The EPA limit excludes radon and uranium, so labs may adjust the result. Ask your lab how they reported it.
Is gross alpha the same as radiation from my home?
It only measures radioactivity in the water sample. Test indoor air separately for radon.
Sources: EPA radionuclides rule; EPA drinking water regulations. Limits checked November 2026.