08/20/2026
4,000. That's the number Maine uses for radon in your water.
Here's the guidance, straight, without spin:
Maine's advisory level for radon in a home's water supply is 4,000 pCi/L. At or above that level, the State recommends you begin by reviewing your total radon risk — air and water together. As the result gets closer to 10,000 pCi/L, the State's guidance moves toward strongly considering treatment.
For radon in indoor air, the advisory level is 4 pCi/L, with Maine CDC recommending you also consider action between 2 and 4.
Two different numbers, two different units, two different tests. Confusing them is the most common mistake we see.
The practical takeaway for a well owner: an air test result tells you nothing about your water result, and vice versa. If you want the full picture, you need both.
Start with the water. Aerus of Brewer's free in-home water test is the first step, and we'll be direct about which concerns — radon included — require accredited laboratory analysis rather than an on-site screening. Call (207) 989-5143 or book online: https://bit.ly/4uJ8T2w