Two Sources, One Problem
Most people know that radon is a gas that seeps into homes from the soil. Fewer know that radon can also enter through well water — and that the two sources require different testing methods and different solutions. If your home uses a private well, you may face both problems simultaneously.
Understanding the difference between airborne radon and waterborne radon is the first step toward protecting your family from both.
Radon in Air: The Primary Risk
Airborne radon is the dominant health concern. Radon gas is produced when uranium — naturally abundant in Maine's granite bedrock — decays in soil and rock formations beneath your home. The gas seeps upward through:
- Cracks in foundation walls and floors
- Gaps around service pipes and utility penetrations
- Construction joints
- Exposed soil in crawlspaces
Once inside, radon accumulates in enclosed spaces, particularly basements and ground-floor rooms. Breathing radon over months and years damages lung tissue, significantly increasing the risk of lung cancer. The EPA recommends fixing any home with air radon at or above 4 pCi/L.
How to test for air radon: Short-term charcoal canisters (48–96 hours) or long-term alpha track detectors (90 days to 1 year) placed in the lowest livable level of the home. Both are inexpensive and widely available.
How to fix it: Active sub-slab depressurization — a fan-powered pipe system that draws radon from beneath the slab and vents it outside. Reduces levels by 50–99%.
Radon in Water: A Secondary but Real Risk
If your home uses a private well (not municipal water), groundwater traveling through radon-producing rock formations can dissolve radon gas and carry it directly into your plumbing. When you use water-intensive appliances — showers, dishwashers, washing machines — this dissolved radon is aerosolized into the air.
This means water-borne radon contributes directly to your indoor air radon levels. Studies suggest that approximately 1 pCi/L of air radon is added for every 10,000 pCi/L of radon in water. If your water has 20,000 pCi/L, it may be adding 2 pCi/L to your air — a meaningful contribution in a home already at 3 pCi/L.
There is also a small but documented risk from directly ingesting radon through drinking water, associated with stomach cancer. The EPA has proposed a Maximum Contaminant Level (MCL) of 300 pCi/L for radon in public water supplies, and suggests a similar benchmark for private wells.
How to test for water radon: A water sample must be collected and sent to a certified laboratory. Unlike air radon kits, water testing is not something you can do with a home test kit — sample collection technique matters, and the analysis requires specialized equipment.
How to fix it: Aeration treatment systems that bubble air through water to drive off dissolved radon are the most effective solution (80–99% removal). Activated carbon (GAC) filters are effective for lower levels but require more maintenance and eventual safe disposal of the radioactive filter media.
Side-by-Side Comparison
| Factor | Radon in Air | Radon in Water |
|---|---|---|
| Primary source | Soil and bedrock beneath home | Groundwater from private well |
| Entry path | Foundation cracks, gaps, porous concrete | Household plumbing; released during water use |
| Health risk | Lung cancer (primary risk) | Lung cancer from re-aerosolized gas; stomach cancer from ingestion |
| Action level (EPA) | 4 pCi/L in air | ~300–4,000 pCi/L in water (varies by guideline) |
| Test method | Charcoal canister or alpha track detector | Lab water sample (certified lab required) |
| Primary fix | Sub-slab depressurization system | Aeration system or activated carbon filter |
| Who is at risk | All Maine homeowners | Homeowners with private wells only |
Do You Need to Fix Both?
If your air radon is elevated and you have a private well, it's worth testing the water to understand whether it's contributing to air radon levels. However, addressing air radon first (with a mitigation system) is usually the highest priority, since the direct inhalation risk from soil-sourced radon is typically larger than the contribution from water.
If water radon is very high (10,000+ pCi/L), treating the water is important both to reduce the contribution to indoor air and to address the ingestion risk directly.
In some homes, both systems are installed together. Our team can assess your specific situation — air test results, water well type, and home construction — and recommend whether one or both interventions are needed.
Maine-Specific Considerations
Maine's granite geology makes it one of the highest-radon states in the country. The same formations that cause elevated air radon also affect groundwater. A significant percentage of Maine homes rely on private wells, making waterborne radon a relevant concern for a large portion of the state's population.
Maine's Department of Health and Human Services recommends that homeowners with private wells test both air and water radon levels, particularly in granite-rich regions of central and western Maine.
Not Sure Which Problem You Have?
We can help you understand your test results and recommend the right solution for your home — whether that's air mitigation, water treatment, or both.
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