ResourcesGlossary: radon in water
Granular activated carbon
Short answer
Granular activated carbon, GAC for short, is a filter material used to take radon out of well water where the water enters the home. EPA puts its typical reduction at 85 to 95 percent.
What granular activated carbon means
EPA sets out the trade. GAC is less efficient for higher levels than aeration and is for moderate levels, around 5,000
The radon it catches does not vanish. EPA says radioactive radon by-products can build on the carbon, that the tank may need a radiation shield and care in disposal, and that while GAC filters usually cost less than aeration systems, filters can collect radioactivity and may require a special method of disposal.
What carbon leaves in the water
Each row applies both ends of EPA's typical reduction for GAC to a level of radon in well water.
| Water before treatment, pCi/L | EPA's typical reduction | After the filter, pCi/L in water |
|---|---|---|
| 2,000 | 85 to 95 percent | 300 to 100 |
| 4,000 | 85 to 95 percent | 600 to 200 |
| 5,000 | 85 to 95 percent | 750 to 250 |
What it means for your home
A filter at the kitchen tap is not this. EPA says point-of-use devices treat only a small portion of the water you use and are not effective in reducing the risk from breathing radon released into the air from all the water used in the home.
Both treatments have advantages and disadvantages that EPA says should be discussed with your state radon office or a water treatment professional.
Where to go next
- Radon in water treatment costs. What a carbon system costs beside an aeration system.
- How to get radon out of water. The two treatments that work, and the ones that do not.