Consumer's Guide to Radon Reduction - Radon in Water

A man at a well.

Well owners with elevated indoor radon levels should test their well water for radon. Radon in your water supply can increase your indoor radon level, although, in most cases, radon entering the home through water will be a small source of risk compared with radon entering from the soil.

EPA estimates that indoor radon levels will increase by about 1 pCi/L for every 10,000 pCi/L of radon in water. You can find publications and documents developed by EPA's Office of Ground Water and Drinking Water relating to radon in drinking water and the radon in drinking water rule.

What Do the Results of Your Water Test Mean?

Estimate how much the radon in your water is elevating your indoor radon level by subtracting 1 pCi/L from your indoor air radon level for every 10,000 pCi/L of radon that was found in your water. (For example: if you have 30,000 pCi/L of radon in your water, then 3 pCi/L of your indoor measurement may have come from radon in water).

If most of the radon is not coming from your water, fix your house first and then retest your indoor air to make sure that the source of elevated radon was not your private well. If a large contribution of the radon in your house is from your water, you may want to consider installing a special water treatment system to remove radon. EPA recommends installing a water treatment system only when there is a proven radon problem in your water supply.

How is Radon Removed From Water?

Radon can be removed from water by using one of two methods: aeration treatment or granular activated carbon (GAC) treatment. Aeration treatment involves spraying water or mixing it with air, and then venting the air from the water before use.

GAC treatment filters water through carbon. Radon attaches to the carbon and leaves the water free of radon. The carbon may need special handling in its disposal if it is used at a high radon level or if it has been used for a long time. In either treatment, it is important to treat the water where it enters your home (point-of-entry device) so that all the water will be treated.

Point-of-use devices, such as those installed on a tap or under the sink, will only treat a small portion of your water and are not effective in reducing radon in your water. It is important to maintain home water treatment units properly because failure to do so can lead to other water contamination problems. Some homeowners opt for a service contract from the installer to provide for carbon replacement and general system maintenance.

Refer to the Installation and Operating Cost Table for more information on water treatment systems.

Installation and Operating Cost Table
Technique Typical Radon Reduction Typical Range of Insulation Costs
Typical Operating
Cost Range for Fan
Electricity & Heated/
Cooled Air Loss
Subslab Suction
(Subslab Depressurization)
80-99% $800-$2,500 $75-$175 Works best if air can move easily in material under slab.
Passive Subslab Suction 30-70% $550-$2,250 There may be some energy penalties May be more effective in cold climates; not as effective as active subslab suction.
Draintile Suction 90-99% $800-$1,700 $75-$175 Works best if drain tiles form complete loop around house.
Blockwall Suction 50-99% $1,500-$3,000 $150-$300 Only in houses with hollow block walls; requires sealing of major openings.
Sump Hole Suction 90-99% $800-$2,500 $100-$225 Works best if air moves easily to sump under slab; or if drain tiles form complete loop.
Submembrane Depressurization in a crawl space 80-99% $1,000-$2,500 $70-$175 Less heat loss than natural ventilation in cold winter climates.
Natural Ventilation in a crawl space 0-50% none
($200-$500 if additional vents installed)
There may be some energy penalties. Costs vary.
Sealing of Radon Entry Routes 0-50% $100-$2,000 None Normally used with other techniques; proper materials and installation required.
House (Basement) Pressurization 50-99% $500-$1,500 $150-$500 Works best with tight basement isolated from outdoors and upper floors.
Natural Ventilation Variable None
($200-$500 if additional vents installed)
$100-$700 Significant heated/cooled air loss; operating costs depend on utility rates & amount of ventilation.
Heat Recovery Ventilation 25-50% if used for full house;
25-75% if used for basement
$1,200-$2,500 $75-$500 for continuous operation Limited use; best in small houses; for full house, use with levels no higher than 8 pCi/L; no higher than 16 pCi/L for use in basement; less conditioned air loss than natural ventilation.
Water Systems: Aeration 95-99% $3,000-$4,500 $40-$90 More efficient than GAC; requires annual cleaning to maintain effectiveness & to prevent contamination; carefully vent system.
Water Systems: Activated Carbon (GAC) 85-99% $1,000-$2,000 None Less efficient for higher levels than aeration; use for moderate levels (around 5,000 pCi/L or less); radon by-products can build on carbon may need radiation shield around tank & care in the disposal.
*NOTE: The fan electricity and house heating/cooling loss cost range is based on certain assumptions regarding climate, your house size, and the cost of electricity and fuel. Your costs may vary. Numbers based upon 1991 data.