Overview page
Well water and radon
Why private wells are the main concern for waterborne radon, and what public water treatment changes about that risk.
Open the pageWater11 min read
Radon in water: wells, health risk, testing and treatment
Short answer
Radon in water comes from uranium in the rock around a well; it is mainly a concern for private wells and other groundwater, and most of its risk comes from radon released into the air when water is used for showering, laundry and dishes. The radon from soil is usually a much larger risk, so test the air first, then test a private well's water, and treat it with aeration or a carbon filter if the level is high.
Key takeaways
- Radon dissolves into groundwater from uranium-bearing rock, so private wells and public systems that use groundwater are where it is found; surface water rarely carries much.
- Most of the risk is breathing radon released from tap water, not drinking it. Soil gas is usually a much larger source than water.
- About 10,000 pCi/L of radon in water adds about 1 pCi/L to indoor air, by the estimate state health and extension programs use.
- There is no federal limit for radon in private well water. Vermont and Maine use 4,000 pCi/L as the point to act or look harder.
- Treatment is at the point of entry: aeration or granular activated carbon. A filter at one tap does not address the air.
In a picture · 1 min read
What radon in water is
Radon in water is radon gas dissolved in a home's water supply. The radon in a home's air can come from two sources, the soil or the water supply, and the soil is usually by far the larger. Water becomes a source when it comes from the ground: radon can get into drinking water when a well is drilled into or near rock formations that contain uranium.
- Cracks in solid floors
- Construction joints
- Cracks in walls
- Gaps in suspended floors
- Gaps around service pipes
- Cavities inside walls
- The water supply
Read moreA paragraph, 1 min
Like radon in air, it cannot be sensed. You cannot see, smell or taste radon, and testing is the only way to know if it is in your drinking water. This page covers the whole topic; radon in well water, water testing and water treatment each go deeper.
At a glance · 1 min read
How radon gets into water
Radon comes from the decay of uranium in the earth's crust. When it is released from underground rocks such as granites or shales, radon can move easily toward the surface in air or water, and groundwater sources such as springs, wells and boreholes normally carry higher radon concentrations than surface water from reservoirs, rivers or lakes. Surface water in contact with the air lets radon escape into the atmosphere.
| Water source | Detail |
|---|---|
| Private wells drilled into granite or other uranium-bearing rock | Where radon in drinking water is primarily a concern; radon can enter a well drilled into or near rock that contains uranium |
| Shallow dug or bored wells | Often not deep enough to reach water in contact with concentrated uranium or radon sources |
| Public systems that use groundwater | A radon problem is more likely than with surface water; some systems treat their water first |
| Small public groundwater systems | Limited survey data suggest smaller systems carry higher concentrations than larger ones |
| Surface water: reservoirs, rivers, lakes | Not usually a problem; normally lower radon than groundwater |
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Read moreA paragraph, 1 min
Even neighbors differ. Two adjacent wells may show very different radon concentrations, and levels in well water can vary through the year. A neighbor's result therefore says little about your well.
At a glance · 1 min read
Is radon in water dangerous? Inhalation vs ingestion
The main danger is the air it creates. Radon in a water supply poses an inhalation risk and a smaller ingestion risk, and most of the risk from radon in water comes from radon released into the air when water is used for showering and other household purposes. Research has shown that the lung cancer risk from breathing radon in air is much larger than the stomach cancer risk from swallowing water with radon in it.
| Pathway | Detail |
|---|---|
| Breathing radon released from water | The most important pathway; showering, washing dishes and doing laundry release radon into indoor air |
| Drinking it | Over a lifetime, a small risk of stomach cancer |
| What studies show on ingestion | Studies have not confirmed an association between drinking water containing radon and a higher risk of stomach cancer |
Read moreA figure and two paragraphs, 1 min
Agency estimate
89 percent
Of the about 168 cancer deaths a year EPA estimated in 1999 that radon in drinking water causes, the share from lung cancer from breathing radon released from water; the other 11 percent were stomach cancer from drinking it
EPA has put numbers on the two pathways. Based on a 1999 National Academy of Sciences report on radon in drinking water, EPA estimated that radon in drinking water causes about 168 cancer deaths a year, 89 percent from lung cancer caused by breathing radon released from water and 11 percent from stomach cancer caused by drinking water that contains radon. The same 1999 fact sheet says only about 1 to 2 percent of the radon in indoor air comes from drinking water, and Connecticut's health department adds that radon escapes from water into the air during household water use, especially when the water is heated.
Put plainly, the vast majority of radon-related health risk is from breathing radon. How radon harms the lungs is covered in the radon and lung cancer guide.
Key figures · 1 min read
How much radon in water adds to the air
Agency estimate
10,000 to 1
10,000 pCi/L of radon in water adds about 1 pCi/L to a home's air, by the common estimate
Read moreTwo paragraphs and a table, 1 min
That ratio is the bridge between the two numbers. A worked example: 4,000
| Radon in water | Added to indoor air, about |
|---|---|
| 1,000 pCi/L | 0.1 pCi/L |
| 4,000 pCi/L | 0.4 pCi/L |
| 10,000 pCi/L | 1 pCi/L |
| 40,000 pCi/L | 4 pCi/L |
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The arithmetic is an average estimate, not a measurement of your home. Air and water radon are separate: soil gas radon does not predict well water radon, nor the reverse. EPA recommends fixing a home when the radon level is 4 pCi/L or higher.
At a glance · 1 min read
Who should test water for radon
Test the air first. Although radon gets into some homes through water, it is important to first test the air, and if you find a radon problem in the air and your water comes from a well, have the water tested. Well owners who are concerned can go further and test for radon in both air and water, so they can weigh the
| Your water | What to do |
|---|---|
| A private well, air tested high | Test the water |
| Any private well | Test the water; Maine recommends it for all homes with wells, and Georgia for every drilled well above its Fall Line |
| A public supply from groundwater | Ask your water supplier; some public systems treat for radon |
| A public supply from surface water | Radon is not usually a problem |
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Read moreA paragraph, 1 min
Air tests and water tests use different devices and procedures. How water is sampled is on water testing, and the air test on radon testing.
At a glance · 2 min read
Acceptable radon level in water: what a result means
There is no federal number for private wells. At present no action level is set at the federal level for radon in drinking water, and as of 2015 EPA had set no maximum contaminant level for it. Some states set their own, and those that have set limits put them between 4,000 and 10,000 pCi/L.
| Proposed level | Figure | What it was for |
|---|---|---|
| Maximum contaminant level goal (MCLG) | Zero | A non-enforceable goal |
| Maximum contaminant level (MCL) | 300 pCi/L | A community water system with no multimedia mitigation program for indoor air |
| Alternative maximum contaminant level (AMCL) | 4,000 pCi/L | A community water system covered by a state or local multimedia mitigation program |
| Who it would have covered | Community water systems | Systems using ground water or mixed ground and surface water; not systems using only surface water, and not private wells |
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Read moreTwo paragraphs and a table, 1 min
The two figures most often quoted, 300 and 4,000 pCi/L, come from a proposal. On November 2, 1999, EPA proposed a radon in drinking water rule for community water systems that use groundwater: a maximum contaminant level (MCL) of 300 pCi/L, and an alternative maximum contaminant level (AMCL) of 4,000 pCi/L for systems where the state, or the water system itself, runs a multimedia mitigation program to reduce radon in indoor air. The proposed goal was zero, which EPA called a non-enforceable goal. The proposal would not have applied to private wells, because EPA does not regulate them.
| Result | Vermont | Maine | Connecticut | Georgia extension lab |
|---|---|---|---|---|
| Below 300 pCi/L | Under the advisory level | Under the guideline | Under the action level | Low; no considerable health risk from ingestion |
| 301 to 4,000 pCi/L | Under the advisory level; test again in five years | Under the guideline | Under the action level | Slightly elevated; treatment may be considered |
| 4,000 to 10,000 pCi/L | At or above 4,000: take action to reduce radon | Weigh all radon sources and decide which to reduce; more important as levels rise | At or above 5,000, the average of two samples: take action; carbon works below 10,000 | Treatment with carbon or aeration recommended |
| Above 10,000 pCi/L | Take action | Strongly consider fixing the water | Aeration, the only effective method at or above 10,000 | Aeration recommended |
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You need your air result too: if the air has not been tested, test it before deciding how to reduce radon, and test the air whatever the water result.
In a picture · 1 min read
Radon water filtration and treatment: how radon is removed
Radon is treated where water enters the house. Point-of-entry treatment removes radon before the water reaches the home's pipes and usually uses granular activated carbon (GAC) filters or aeration systems; both are straightforward and effective techniques. Point-of-use devices treat water at one tap, such as drinking water, and do not reduce the risk from radon released into the air from all the water used in the home.
Typical radon reduction, EPA
Radon in private well water
- Private well water: aeration95 to 99 percentGenerally more efficient than GAC; requires annual cleaning to maintain effectiveness and to prevent contamination; requires venting radon to outdoors.
- Private well water: granular activated carbon (GAC)85 to 95 percentLess efficient for higher levels than aeration; use for moderate levels, around 5,000 pCi/L or less in water.
Read moreA table and a paragraph, 1 min
| Feature | Aeration | Granular activated carbon (GAC) |
|---|---|---|
| Typical reduction | 95 to 99 percent | 85 to 95 percent |
| Best for | Generally more efficient; recommended above 10,000 pCi/L | Moderate levels, around 5,000 pCi/L or less |
| Upkeep | Annual cleaning; radon is vented outdoors | Carbon replaced regularly; decay products can build up and need special disposal |
| Installed cost, Georgia extension estimate | ~$4,000 installed | ~$1,000 installed |
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Which one fits depends on the level. Connecticut's health department says carbon (GAC) filtration reduces radon effectively when levels are below 10,000 pCi/L, and that aeration is the only effective method at or above 10,000 pCi/L. Vermont discourages GAC for radon because the radon collected on the filter could create a radiation hazard. Details, certification and upkeep are on radon water treatment.
Overview · 1 min read
Radon in public water supplies
If your water comes from a public system and you are concerned, contact your water supplier; some public water systems treat their water to reduce radon before delivering it. The risk from a public system sourced from groundwater is considered lower than from a private well, so ask your provider whether it tests for radon.
Read moreA note, 1 min
Overview · 1 min read
Radon in water and a home sale
If you have tested the air, found elevated levels, and the water comes from a private well, have the water tested before a sale. Some states regulate who may test: in Maine, a Maine registered radon tester must do the test unless the owner or occupant does it, it is illegal for a realtor or home buyer to do a radon in air or radon in water test, and a home for sale needs an independent registered tester.
Questions · 3 min read
Radon in water questions
Is radon in well water dangerous?
Mainly through the air. Radon released from showers, laundry and dishes raises indoor radon, and breathing radon is the main lung cancer risk. Swallowing it carries a much smaller risk.
Is it safe to drink water with radon?
The ingestion risk is small compared with breathing radon in air, and studies have not confirmed a link between drinking water with radon and stomach cancer, though drinking it over a lifetime carries some risk of stomach cancer.
What level of radon in water is safe?
There is no federal limit for private wells. Vermont's advisory level is 4,000 pCi/L; Maine uses 4,000 pCi/L as a guideline and says to strongly consider treatment around 10,000 pCi/L; Connecticut's recommended action level is 5,000 pCi/L.
Where do the 300 and 4,000 pCi/L radon in water figures come from?
From a proposal. In 1999 EPA proposed a maximum contaminant level of 300 pCi/L for community water systems that use groundwater, and an alternative level of 4,000 pCi/L where a multimedia mitigation program reduces radon in indoor air. The proposal would not have applied to private wells, and as of 2015 EPA had set no maximum contaminant level for radon in drinking water.
Should I test my well for radon?
Yes, if your air tests high and you have a well, and many states recommend it for every home with a well.
How much radon from water gets into the air?
About 1 pCi/L in the air for every 10,000 pCi/L in the water, by the common estimate.
Does city water have radon?
Water from surface sources usually does not. Public systems that use groundwater can, and some treat it; ask your water supplier.
Does boiling or distilling water remove radon?
Neither is a treatment the agencies here recommend. Boiling and distilling both heat water, and Connecticut's health department says radon escapes from water into the air during household water use, especially when the water is heated. The treatments named for a home's water are aeration and granular activated carbon, at the point where water enters the house.
Does a Brita or other pitcher filter remove radon?
A pitcher filter treats only the water poured through it, which makes it a point-of-use device. EPA says point-of-use devices treat only a small portion of the water you use, such as the water you drink, and are not effective in reducing the risk from breathing radon released into the air from all water used in the home. Whether a particular filter removes radon from the water it treats is for its maker to state; the treatments agencies name for a home's water are point-of-entry aeration and whole-house granular activated carbon.
Does a radon mitigation system remove radon from water?
No. Soil suction treats soil gas under the house. Radon in water is treated at the point of entry with aeration or carbon.
Can a water filter remove radon?
A whole-house granular activated carbon filter can, with a typical reduction of 85 to 95 percent. A filter at one tap does not address radon released into the air elsewhere in the home.
Can radon in water change over time?
Yes. Radon in well water can vary through the year, so testing more than once at different times gives a better picture.
Do I need to treat water if my air radon is high?
Not necessarily. Air and water radon are separate, and soil gas is usually the larger source. Test both, then weigh your risk from each source and deciding which is most important to reduce.
Water
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Radon in well and household water: when it matters, how a water test works, and treatment.
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How aeration and granular activated carbon systems reduce radon in water, and how they differ from soil-gas mitigation.
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