Does Reverse Osmosis Remove Radon from Drinking Water?

Does Reverse Osmosis Remove Radon from Drinking Water?

Radon is a radioactive gas that is found in some groundwater. It is considered a health hazard and can cause lung cancer if you are exposed to it over a long period of time. Some people may be concerned that radon may be present in their drinking water. If you are one of these people, you may be wondering if reverse osmosis can remove radon from your water.

Reverse osmosis does not remove most dissolved gases including radon. Residential RO filters typically have a carbon pre-filter that removes radon. However, the membrane is the primary method of treatment with reverse osmosis systems, not the carbon filter. You should use a more appropriate treatment method such as carbon filtration or aeration for radon removal.

In this blog post, we will discuss using reverse osmosis to remove radon from drinking water. Although RO is not effective at removing radon gas, it offers many other advantages and benefits that are worth considering. Continue reading to learn more about using RO to remove radon from your water.

About Radon

Here’s what you should know about radon, its health risks and how to protect yourself from them.

  • Radon is a naturally occurring gas that has no color or smell
  • It can dissolve into water posing an issue for both private drinking supplies as well public utilities
  • There are 30 to 1,800 deaths per year caused by radon in drinking water

What is radon?

Radon is a decay product of naturally occurring uranium, radium, and thorium. Radon exposure typically occurs when individuals inhale the gas.

Showering, washing dishes, and doing laundry can all release radon gas into the air you breathe. You can also be exposed to radon if you drink water that contains it. Radon exposure typically happens indoors in places like homes, schools and workplaces.

EPA Map of Radon Zones

There is very little radon in surface water, such as lakes and rivers. Public water supplies do not generally have radon in them. The primary issue with radon in drinking water is associated with private wells.

Each year there are 30 to 1,800 deaths in the United States due to radon from household water. Drinking water containing radon also presents a risk of developing internal organ cancers (i.e., stomach cancer). The health risks for ingesting radon in drinking water are smaller than the risks of inhaling radon gas. Needless to say, radon can cause cancer.

Breathing high concentrations of radon is linked with lung cancer. Researchers and the United States Environmental Protection agency (EPA) estimate it causes 12,900 – 21,000 lung cancer deaths per year in the United States. This makes it the second most frequent cause of lung cancer (cigarette smoking is the most frequent cause). There are synergistic effects of radon and smoking – that is, if you smoke and inhale radon, you’re at a greater risk of lung cancer. Of the annual lung cancer deaths due to radon, about 2,900 of these deaths are people who have never smoked though.

Health concerns with radon

The main health risk associated with radon is lung cancer. Studies in miners have shown that long-term, high-level exposure to radon can lead to an increased risk of developing lung cancer.

According to the US EPA, the second leading cause of lung cancer in the United States is radon gas. Nationally, it’s estimated that about 21,000 people die each year from this preventable disease due to their exposure to radon.

Drinking water with radon in it can also lead to an increased risk of developing stomach cancer. The health risks from ingesting radon in drinking water are generally much smaller than the risks from inhaling radon gas.

Drinking water standard for radonRadon Risk Levels graphic

There is currently no federal drinking water standard for radon. These standards, known as a maximum contaminant level (MCL), are established by the EPA.

Several states have established guidelines for radon in drinking water. The following table summarizes several state standards for radon in drinking water.


5,000 pCi/L


10,000 pCi/L


10,000 pCi/L


4,000 pCi/L

Rhode Island

4,000 pCi/L

Reverse Osmosis

reverse osmosis filter system to remove viruses from drinking water

Reverse osmosis, or RO, is a type of water filtration technology that is used to remove impurities from water. It works by forcing contaminated water through a semipermeable membrane. The membrane has small holes, called pores, that allow water molecules to pass through, but block contaminants.

RO systems can remove a variety of impurities from water very well. This technology works very well for dissolved solids like salt and metals. It also works well for suspended solids and large molecules. Reverse osmosis is not effective at removing most dissolved gases.

Read my articles on reverse osmosis to learn more.
The Definitive Guide to Whole House Reverse Osmosis Filter Systems
Complete Guide to Under-sink Reverse Osmosis Filters

How RO works

Reverse osmosis systems use pressure to force water through a semipermeable membrane. The water is forced through the membrane, and the impurities are filtered out. The clean water is then collected on the other side of the membrane, while the contaminants are retained in a concentrated brine. This brine waste is then flushed down the drain.

Reverse osmosis systems can be used to treat both municipal water supplies and private wells. This treatment technology is effective at removing a wide range of contaminants, including salt, bacteria, viruses, pesticides, and more.

RO system components

Residential reverse osmosis systems typically have the following components:

  1. Pretreatment filters: This step consists of a sediment filter to remove particles such as dirt and rust, and an activated carbon filter to remove chlorine and other chemicals.
  2. Reverse osmosis membrane: The reverse osmosis membrane is a thin film composite (TFC) that removes contaminants from water. This is the heart of the RO system.
  3. Post-filter: The post-filter step polishes the water and removes any remaining impurities. This is often a second carbon filter.

Many RO systems have the following additional components to improve their functionality:

  • Storage tank
  • Faucet or dispenser
  • Re-mineralizer

How Well Does Reverse Osmosis Treat radon

Reverse osmosis is not effective at removing radon from drinking water. In general, RO does not remove dissolved gases such as hydrogen sulfide or radon.

As noted above, most RO systems include a carbon pre-filter. Carbon is very effective at removing radon from water. Although reverse osmosis is not effective at removing radon, the carbon filter that comes with your RO system is. As a result, most residential reverse osmosis systems will provide some limited amount of radon removal.

Challenges with radon and RO

The carbon filter in a reverse osmosis system is intended to remove chlorine from the water to protect the membrane from oxidation damage. It wasn’t designed to be the primary method of treatment for radon.

As such, your RO system does not have enough carbon to reliably remove radon from your drinking water over an extended period of time. You may get good radon removal for a few weeks, maybe even a month or two.

However, this small carbon filter will become saturated pretty quickly, and the radon concentrations will increase in your drinking water. You would be better off installing a whole-house carbon filter for radon removal to protect you and your family.

Factors to Consider with Reverse Osmosis

If you’re concerned about radon in your drinking water, a reverse osmosis filter is probably not the best option for you. Reverse osmosis systems can remove a variety of other contaminants from your water, including lead, mercury, and chlorine. However, they aren’t suitable for radon treatment.

Treatment Methods that Remove radon

There are other treatment methods that are much more effective at removing radon from your drinking water, including whole-house carbon filters and aeration systems.

Carbon filters

Carbon adsorption is a water treatment technology that is very effective at removing a wide range of contaminants, including radon. Carbon filters consist of a tank or vessel that is filled with granular activated carbon media. The water is piped through the tank, and the contaminants are adsorbed onto the surface of the carbon media.

Carbon filters can be used as whole-house systems or point-of-use (POU) devices. With radon, you need to remove radon from all of the water in your home, not just the water you drink. This is because the dissolved radon will be released from the water when you shower, do laundry, or even just run the dishwasher.

You and your family are exposed to radon gas through inhalation. Breathing radon is much worse than drinking it, so you need to make sure all of the water in your home is treated for radon.

Read my article on using carbon filters to remove radon from drinking water.

Air stripper (aeration)RadonAway Aeration System

Aeration is another water treatment technology that is effective at removing dissolved gases such as radon from water. Aeration works by bubbling air through the water, which strips out the dissolved gas. The stripped gas is then vented to the atmosphere, and the treated water is collected.

Aeration can be used as a whole-house system or POU device. Like carbon filters, you need to remove radon from all of the water in your home to protect your family from exposure to radon gas.


Does boiling water remove radon

Boiling water will remove some radon, but not all of it. The solubility of radon gas decreases as the water temperature goes up. Boiling the water will cause most of the radon to off-gas.

This can be dangerous because you are exposed to the radon gas in your kitchen. Breathing radon gas is much more dangerous than drinking it. If you are concerned about radon in your water, you should install a whole-house carbon filter or aeration system.

Does a water softener remove radon

Water softeners do not remove radon from drinking water. Water softeners use ion exchange resin to remove hardness minerals from the water. Radon is not removed by the ion exchange resin.

Does activated carbon treat other contaminants in the water?

One benefit of carbon filtration is the fact that it treats a large number of other contaminants. This is a real benefit of installing a carbon treatment system. Carbon also improves the taste of water and removes odor-causing contaminants.

Do carbon filters need maintenance?

Carbon filters require maintenance to keep them operating properly. The carbon media eventually becomes spent and must be replaced. Depending on the size of your carbon system, this is usually once per year. The cost to replace the spent carbon is $400 to $800.

Do aeration systems need maintenance?

Aeration systems require periodic maintenance to keep them operating properly. The frequency of maintenance will depend on the type of system you have, and the water quality conditions in your area. You should expect to have your aeration system serviced once every year. The cost to service an aeration system is $200 to $500.

Will my Water Pressure change if I install a removal system?

GAC systems will reduce water pressure by only a few pounds. An aeration system will change the water pressure to whatever the capacity of the aeration system produces. In many cases the aeration system can produce higher water pressure than previously existed with a well system.

Final Take

In short, while reverse osmosis systems can remove a wide variety of contaminants from drinking water, they are not effective at removing radon. If you’re concerned about radon in your drinking water, we recommend installing a whole-house carbon filter or an aeration system for reliable removal.

Boch Richard

Richard Boch is a chemical engineer responsible for designing water filtration systems for industrial and residential customers. He has more than 20 years of experience with ion exchange, activated carbon, and reverse osmosis. Richard's expertise has made him a go-to source for municipalities and businesses looking to improve their water quality. When he's not working, Richard enjoys spending time with his wife and two young children.

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