Why Radon Mitigation Is Different for Well Water Than for Soil-Based Radon

Confirm the Source Before You Recommend Radon Mitigation

Before you decide how to approach radon mitigation, you have to confirm where the radon is coming from. In many homes, the primary source is soil gas, but in homes with private wells, water can also contribute to indoor radon. I usually recommend starting with an indoor air test because it reflects the exposure risk most directly. If the home uses well water, I also suggest a water test, especially if the air test is elevated.

A key point is that a home can have both sources at once. Even if you have a soil mitigation system installed, radon-in-water may still be elevating the indoor air level. On the flip side, some homes show modest air readings but have high radon levels in the well water, which can still matter. The goal is to match the mitigation method to the actual source, not just the symptom.

Understand How Radon in Well Water Becomes an Indoor Air Problem

Radon in well water becomes an indoor air problem when the water is used and agitated. I explain it to homeowners as a “release” process: when water sprays, splashes, or warms up, dissolved radon can come out of the water and enter the air. Showers tend to be the biggest contributor, but laundry machines, dishwashers, and aerated faucets can also release radon. The more water you use and the more it’s disturbed, the more radon can transfer into indoor air.

This is one reason why two homes with similar water test results may experience different indoor air levels. A house with more occupants, longer showers, and frequent laundry cycles can release more radon than a home with lighter water use. Ventilation matters too, since radon can build up more quickly in tight, newer homes. It’s a good reminder that radon is a “whole home” issue, not just a lab number.

Use the Right Testing Method (Air vs. Water Requires Different Tools)

Radon mitigation decisions are only as good as the testing behind them, so it’s important to test the source you’re trying to address. Indoor air testing and well water testing measure different pathways, and they each require a different approach to get reliable results. I always encourage homeowners not to assume one test tells the whole story, especially in well homes. A quick comparison makes it easier to choose the right next step.

Here’s a simple way to think about testing based on the source:

• Air Testing: Use a short-term (2–7 days) or a long-term test (90+ days) on the lowest livable level of the home.
• Water Testing: Collect the sample carefully, avoid agitation, and ship it quickly to the lab to prevent radon loss.
• Best Practice for Well Homes: Test indoor air first, then test well water so you can confirm whether the water is contributing.

When I collect or guide a radon-in-water sample, I emphasize gentle handling and following the lab’s instructions exactly. It usually means filling the vial carefully, avoiding bubbles, sealing it tight, and shipping it promptly. This isn’t the kind of test you want to rush, because small mistakes can affect the result. Good data up front makes radon mitigation decisions much more straightforward.

Match Radon Mitigation to the Entry Path—Soil Systems Won’t Fix Water Radon

One of the most common misunderstandings I hear is that a soil-based radon system will automatically solve radon-in-water. A standard sub-slab depressurization system is designed to pull radon gas from beneath a foundation and vent it safely outside. It’s highly effective for soil gas because it targets the pressure-driven entry routes through the slab and foundation. But it doesn’t remove radon that’s dissolved in water and later released indoors at fixtures.

That doesn’t mean soil mitigation isn’t important—many homes need it. It just means soil and water are separate pathways that sometimes require separate solutions. If you only address one source while the other is significant, you may still see elevated radon in your follow-up air test. Once you understand the source, the fix becomes much more predictable.

Choose the Correct Well-Water Radon Mitigation Method (Aeration vs. GAC)

When it comes to radon mitigation for well water, there are two common approaches: aeration systems and granular activated carbon (GAC) systems. Both methods can reduce radon in water, but they work differently and fit different scenarios. The right choice depends on the radon level in the water, the household’s water usage, and practical installation considerations. It’s also important to factor in long-term maintenance, not just the initial setup.

At a high level, here’s how these two approaches compare:

• Aeration Systems: Remove radon by stripping it out of water and venting it safely outside.
• GAC Systems: Capture radon in carbon as water flows through the filter.
• In General: Aeration tends to be preferred for higher radon-in-water levels, while GAC can be a good fit for lower levels and simpler installs.

In my experience, homeowners feel best about their choice when they also understand what comes with it long-term. Aeration systems require safe venting and enough space for the equipment, while GAC systems require periodic filter replacement and proper handling. Neither option is “better” in every case; it’s more about choosing the right fit for the home and then maintaining it correctly.

Use GAC for Lower Levels—But Take Filter Safety and Replacement Seriously

Granular activated carbon systems can be a good fit when radon-in-water levels are lower or when space and budget constraints matter. The filter media traps radon as water passes through, which reduces how much radon can later be released into the air at fixtures. These systems are typically compact and simpler to install than aeration. However, the radon collected in the carbon can cause the filter to accumulate radioactivity over time, so placement and maintenance deserve attention.

I always encourage homeowners to treat GAC filters like a component that needs routine oversight, not a permanent fix you forget about. Filters must be replaced on a schedule that matches the water radon level and household use. Disposal rules can vary, so it’s important to follow manufacturer guidance and local requirements. When it’s used in the right context and maintained properly, GAC can be an effective part of a radon mitigation plan.

Watch for “Combo Cases” Where You Need Two Radon Mitigation Systems

In some homes, the most effective approach is a combination of soil mitigation and water treatment. I typically see this when indoor air radon stays elevated after a soil system is installed, or when both the well water and the soil gas levels are clearly contributing. Another situation is a home with heavy water use, where radon released from showers and appliances adds a noticeable bump to indoor air. These combo cases can feel frustrating at first, but they’re very manageable once you identify both sources.

The key is not to assume one system should handle everything. Soil-based systems reduce the pressure-driven entry of radon gas through the foundation. Water systems reduce the radon that enters the home through the plumbing and is released during use. When both sources exist, using both approaches often produces the most consistent results.

Verify Performance After Installation (Testing Is Part of Radon Mitigation)

Radon mitigation should always include verification, because guessing isn’t good enough when health risk is on the line. After a soil-based system is installed, a follow-up indoor air test confirms whether radon levels have dropped into an acceptable range. After a water mitigation system is installed, a follow-up water test verifies the reduction at the well supply point. If the home has both sources, it’s smart to retest both air and water to make sure you’re seeing the full picture.

If you want a simple “done right” check after mitigation, I recommend:

• Retest indoor air after soil mitigation to confirm the reduction.
• Retest well water after water treatment to verify performance at the source.
• Retest both if you addressed both pathways (soil + water).
• Consider a long-term air test for the most reliable view of ongoing exposure.

Long-term testing can be especially useful because radon fluctuates seasonally and with home conditions. Changes like sealing a basement, upgrading windows, or running the HVAC differently can alter indoor radon behavior. A solid radon mitigation plan includes periodic rechecks, so you’re not relying on a single moment in time.

Conclusion

Radon can feel complicated at first, but it becomes much easier to manage when you separate the problem into “soil” and “well water” and choose radon mitigation methods that match each source. If you’re on a private well, testing both air and water is one of the simplest ways to get clarity and avoid chasing the wrong solution. And even after mitigation, I always like to remind homeowners that retesting is part of the process—not because something is likely to go wrong, but because it’s how you confirm peace of mind. If you take it step by step, you can make informed decisions and feel confident about the air you’re breathing and the water you’re using.