Does Reverse Osmosis Remove Radon from Water?

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Radon is a harmful radioactive gas that is sometimes found in groundwater. According to the US EPA, it’s responsible for 21,000 lung cancer deaths yearly. It’s one of those contaminants you should really look out for in your water supply.

Since you obviously know about the risks, you might be wondering if water treatment technologies like reverse osmosis can effectively remove radon from water.

This article will answer your questions, discuss other methods of eliminating radon, and drop tips on how to test your water for radon.

Key Takeaways

  • Reverse osmosis can’t remove radon gas from water. RO membranes are not very effective at removing dissolved gases in general due to their low molecular weight and non-ionic nature.
  • However, a reverse osmosis system for home use with its carbon pre and post-filters can remove up to 99% of radon, provided granular activated carbon (GAC) is being used and you allow for sufficient contact time between water and filter media.

Does Reverse Osmosis Remove Radon from Water?

So, does reverse osmosis remove radon from water?

No, reverse osmosis water purification does not remove radon. This is because radon exists in water as a gas, and reverse osmosis is not very effective at removing gasses.

Although the RO membrane is suited for removing tiny particles and dissolved solids, gaseous molecules are often much smaller than the membrane’s pores and easily slip past the membrane.

In addition, gasses have very low molecular weight and, as in the case of radon, they are not ionically charged. Both are not the best conditions for removal via reverse osmosis water treatment.

Does a Reverse Osmosis System Remove Radon from Water?

But does a reverse osmosis system with its various pre and post-filter stages remove radon from water?

Yes, the activated carbon filters that come with pretty much all reverse osmosis systems can remove radon effectively. In fact, granular activated carbon can remove 99% of radon in water, thanks to the water moving rather slowly through the RO system. This allows for a long contact time between water and filter media, which is exactly what we need.

However, there is one major downside to removing radon using activated carbon filtration, but more on that below.

Under Sink Reverse Osmosis System

What Are the Best Ways to Remove Radon from Water?

Here are some of the most effective ways to remove radon from water:


Aeration is a water treatment technology specifically used to remove dissolved gasses from water. It’s suitable for removing radon, too, since it exists in water as a dissolved gas.

Here’s how aeration works: Air bubbles are introduced into the water to strip out or displace any dissolved gas. The gas is then moved by a vent and released into the atmosphere, while the treated water is collected separately.

Aeration filters come as whole house and point-of-use systems, so you can choose whatever suits your needs.

Granular Activated Carbon

Like I said, carbon filters are effective at removing radon from water. Granular activated carbon (GAC), mainly due to its high adsorption rate, porosity, and large surface area, can remove almost as much as 99% of radon in water – provided you allow for sufficient contact time.

Although GAC filters are a cheaper option for removing radon from water, there’s the issue of disposing of the filter media after use. As the GAC filter traps more and more radon, it becomes increasingly radioactive and unsafe to handle. This calls for extreme carefulness when disposing of old filters. Some state authorities even advise against radon filtration using GAC.

So if you decide to still use this method, contact a professional to help you properly dispose of the used filters – don’t try to do it on your own.


This is another way to remove radon from water. Usually, distillation involves boiling water until it evaporates completely, leaving any contaminants behind. The steam is cooled down in a coil where it turns back into liquid. The distilled water is then collected in a small tank.

When it comes to radon removal, the gas evaporates with the water. Thus, it’s either fanned out or trapped in a carbon post-filter sachet.

Distillation can eliminate nearly 100% of the radon in your water.

The only downside is that it takes very long to distill water and it’s not feasible for large-scale use.

What Is Radon?

Radon is a naturally occurring radioactive gas often found in groundwater and sometimes air. It’s a product of the radioactive decay of uranium, radium, and thorium, which occur naturally in soil and some rocks.

Radon is a colorless, odorless, and inert gas. It has a short half-life of four days and is referred to as a rare gas. It also has radioluminescence qualities, meaning it can emit light after exposure to ionizing radiation.

Radon is highly soluble in water.

Where Does the Radon in Our Water Come from?

Radon is naturally present in rocks and soil. As a result, it can sometimes diffuse into the groundwater surrounding such rocks and then build up in reservoirs like private wells, springs, or boreholes.

When water collected from such sources is used for cooking, showering, washing dishes, or cleaning, radon escapes into the air. This poses a severe issue since radon is more dangerous when inhaled than ingested in drinking water.

Why Is Radon a Health Concern?

Radon as a radioactive gas is a serious health concern. Radon’s radioactive particles accumulate in the body after exposure leading to many potential health risks, including lung and stomach cancer.

Inhaling radon is much more dangerous than ingesting it in drinking water, though. In addition to lung cancer, long-term exposure also increases the risk of leukemia (blood cancer).

Although these health effects are not immediate, long-term exposure to radon may result in symptoms such as:

  • Loss of appetite
  • Weight loss
  • Fatigue
  • Coughing up blood
  • Frequent pneumonia or bronchitis
  • Wheezing
  • Difficult swallowing
  • Frequent sore throat
  • Chest pain
  • Persistent cough
  • Trouble breathing

Drinking Water Standard for Radon

No specific standard or permissible limit has been set to determine the amount of radon allowed in water. However, the EPA recommends 4 pCi/L as a guideline for the maximum level that should be present in the water supply of US residents.

The Environmental Protection Agency further encourages individuals to reduce the limit to 2 pCi/L if possible, since radon in soil and air also contributes significantly to the radon we’re exposed to in daily life.

How to Test for Radon in Water

Water Testing Report

The EPA recommends that you first test for radon in your air before testing for radon in water. This is because any radon found in the air is a more significant health concern.

Regardless, Here are some tips for testing for radon in your water supply:

  1. If your water supply comes from a groundwater source, you can ask your supplier if they’ve tested the water for radon or, better still, request the latest consumer confidence report.
  2. You should check your well water for radon at random intervals if you have a private well. To test your water, take a sample to an EPA-certified laboratory. Lab tests provide the most accurate results and are safer when you’re dealing with gasses as dangerous as radon. DIY radon test kits are often hard to find.

If you have any thoughts about the question, does reverse osmosis remove radon, please don’t hesitate to leave a comment below!

About the Author Alexandra Uta

Alex is a content writer with an affinity for research and a methodical attention to detail. Since 2020, she has fully immersed herself into the home water treatment industry only to become an expert herself. Alex has been using water filters and similar products for years which has gained her lots of hands-on experience.
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