What is the EPA limit for radium in drinking water?

The EPA maximum contaminant level for combined radium-226 and radium-228 is 5 pCi/L (picocuries per liter), set in the 2000 Radionuclides Rule. There is also a separate limit of 15 pCi/L for gross alpha particle activity, which is a broad screen that excludes radon and uranium. Many labs run the gross alpha screen first, and a result above 5 pCi/L on that screen usually triggers a specific radium test. Both limits apply to public water systems. Private wells have no such oversight, so a private well is only tested if the owner pays for it.

How does radium get into well water?

Radium in well water is almost always natural, not from pollution. It forms from the radioactive decay of uranium and thorium in rock and soil. As groundwater moves through certain aquifers, especially sandstone and granite formations, it dissolves small amounts of radium. The USGS has documented elevated radium in specific aquifers, including the sandstone aquifer of the Northern Midwest and parts of the Piedmont and Coastal Plain in the East. Levels vary sharply by location and even between neighboring wells, because the rock each well taps is what matters.

Is radium in drinking water dangerous?

Radium is a known human carcinogen. The main concern is long-term ingestion, because radium behaves chemically like calcium and the body deposits it in bone, where its radiation is linked to bone cancer and related effects over years of exposure. The risk comes from sustained exposure over time, not a single glass. The EPA set its 5 pCi/L combined radium limit because of this long-term cancer risk. This page is general information, not medical advice, so discuss specific health concerns with your doctor or health department.

What does a gross alpha result on my water test mean?

Gross alpha is a screening measurement of total alpha radiation in the water, not a specific contaminant. The EPA limit is 15 pCi/L, measured excluding radon and uranium. Because radium emits alpha particles, a high gross alpha result is often the first sign of a radium problem, and it is usually the cheaper test a lab runs first. If your gross alpha comes back elevated, the next step is a specific test for radium-226 and radium-228 and often uranium, so you know which radionuclide is driving the number and how to treat it.

How do you remove radium from well water?

Radium carries a positive charge, so cation exchange removes it. A standard water softener will reduce radium as a side effect of softening, and dedicated cation exchange or reverse osmosis systems also work. This is the opposite of uranium, which is negatively charged and needs anion exchange or RO. Because both ion exchange resin and RO reject brine can concentrate radium, spent resin and reject water should be handled following your state guidance. Confirm any system with a post-treatment lab test, since radium gives you no taste or smell to tell you whether it is working.

Radium and Gross Alpha in Well Water: The Radionuclide Most Well Owners Never Test For

Health disclaimer: This page provides general educational information about radium and gross alpha in well water. Radium is a known carcinogen. This is not medical or radiation safety advice. If you are concerned about your exposure, contact your doctor, your state health department, or a certified water professional.

If a private well lab report ever flags your water, the line that says “gross alpha” or “combined radium” is the one most homeowners have never heard of and have no idea what to do about. Radon gets the attention because it is a gas you breathe in the shower. Uranium gets its own page because it is a heavy metal. Radium sits between them, quietly, and it is the radionuclide a well actually gets cited for more often than either.

Radium is natural, invisible, and a known carcinogen. It is also testable and treatable. The trap is that almost nobody tests a private well for it until a report forces the question.

What Radium Is and How It Differs From Radon and Uranium

Radium is a naturally occurring radioactive metal. It forms from the slow decay of uranium and thorium that already sit in rock and soil. As groundwater moves through certain rock formations, it dissolves a little radium along the way. There is no factory or dump required. The source is the geology.

That makes radium part of the same family as two contaminants this site already covers, but it behaves differently from both:

Radon is a gas. The main risk is breathing it, not drinking it, because it escapes from water into your indoor air when you shower or run the dishwasher. Radium is a dissolved metal that stays in the water, so the risk is ingestion.
Uranium is a heavy metal whose main concern is chemical toxicity to the kidneys. Radium’s concern is its radioactivity and where the body puts it.

The two are chemically opposite in a way that matters for treatment. Radium carries a positive charge. Uranium in water carries a negative charge. A system built to remove one will not necessarily touch the other, which is why a single lab report can list both and require two different answers.

The EPA Limits: Combined Radium, Gross Alpha, and Uranium

The numbers come from the EPA’s 2000 Radionuclides Rule, part of the National Primary Drinking Water Regulations. Three limits show up on radionuclide reports, and it helps to know what each one means:

Combined radium-226 and radium-228: 5 pCi/L. This is the radium standard. It adds the two radium isotopes together, which is why a report often lists each one plus a combined figure. Picocuries per liter (pCi/L) is the unit for radioactivity in water.
Gross alpha particle activity: 15 pCi/L. This is a screen, not a single contaminant. It measures total alpha radiation in the water, excluding radon and uranium. Because radium emits alpha particles, a high gross alpha result is usually the first hint of a radium problem.
Uranium: 30 ug/L. A separate limit in the same rule, covered in detail on the uranium page.

These limits apply to public water systems, which have to monitor and treat to meet them. Private wells have no such requirement. A private well is only tested when the owner decides to pay for it, which is the entire reason radium goes undetected for so long in well country.

Why Gross Alpha Is Usually the First Number You See

Most certified labs run the gross alpha screen before a specific radium test, because it is cheaper and it catches the alpha-emitting radionuclides as a group. The practical sequence usually looks like this:

The gross alpha screen comes back. If it is comfortably under 5 pCi/L, radium is generally not a concern and no further radionuclide testing is needed.
If gross alpha is elevated, the lab follows up with a specific test for radium-226 and radium-228, and often uranium, to identify which radionuclide is driving the number.
That specific result tells you whether you are over the 5 pCi/L combined radium limit and what kind of treatment fits.

So if a report hands you a high gross alpha figure and nothing else, it is not the final word. It is the flag that says: test for radium next.

The Health Concern: A Bone-Seeking Carcinogen

Here is the part that separates radium from a nuisance contaminant. Radium is chemically similar to calcium, so when you ingest it over a long period, the body treats it like a bone mineral and deposits it in the skeleton. Once there, its radiation acts on bone tissue. The EPA classifies radium as a known human carcinogen, with long-term ingestion linked to bone cancer and related effects.

The risk is about sustained exposure over months and years, not a single drink, which is the same pattern seen with arsenic and uranium. There is no need to panic over having used the water. But there is good reason not to leave an elevated level in place, because the exposure continues for as long as the water does. The EPA set the 5 pCi/L combined radium limit specifically to hold this long-term cancer risk to an acceptable level.

This page is general information, not medical advice. If your water has tested high for radium and you have specific health questions, those belong with your doctor or your state health department, who can advise based on your situation and exposure history.

Who Is at Higher Risk

Radium is a private well issue tied to local geology. The USGS has mapped where it tends to show up in groundwater, and the pattern follows the rock:

The sandstone aquifer of the Northern Midwest, parts of Wisconsin, Illinois, Iowa, and neighboring states, is one of the better-documented radium areas in the country.
Parts of the Piedmont and Coastal Plain in the East, where certain crystalline and sedimentary formations carry uranium and thorium that decay into radium.
Other scattered regions with uranium-bearing or granite bedrock, since those rocks are the parent material radium comes from.

Within any of these areas, levels differ from one well to the next depending on the specific formation each well taps and how deep it draws. A neighbor’s clean test does not clear your well, and your own clean test years ago does not guarantee today’s number. If you are on a private well in a known radium region and you have never specifically tested for it, you do not know your level.

Testing

There is no way to see, taste, or smell radium, so a laboratory test is the only way to know. The practical, lower-cost starting point for most well owners is the gross alpha screen, with a specific radium-226 and radium-228 test as the follow-up if gross alpha comes back elevated.

To find a certified lab, contact your state health department, which can also tell you whether your area is a known radium region and whether subsidized testing is available for well owners. If you are mapping out a full well testing plan rather than chasing a single number, the well water testing guide covers which tests make sense by location and well type, and our roundup of mail-in water tests covers the lab options. Confirm before you order that the test reports radionuclides, since standard well panels for bacteria and nitrate do not include them.

Treatment

Radium responds well to treatment, and the chemistry is the helpful part. Because radium carries a positive charge, cation exchange removes it.

Water softeners (cation exchange). A conventional softener swaps positively charged hardness minerals for sodium, and it reduces radium as a side effect of that same process. For homes that already soften their water, this can lower radium across the house. The catch is that the radium concentrates in the resin and in the brine the softener discharges, so spent resin and backwash should be handled according to your state guidance for low-level radioactive material.
Reverse osmosis (NSF/ANSI 58). An RO system reduces radium at the point of use, making it a strong choice for drinking and cooking water at one tap. As with the softener, the reject water can concentrate radium and should be managed per local guidance. Check the certificate for the specific model and confirm radium is in its scope.
Dedicated cation exchange. Systems built specifically for radium use the same positive-charge chemistry as a softener but are designed and sized for the job.

This is exactly opposite to uranium, which needs anion exchange or RO because it is negatively charged. If a single report flags both radium and uranium, you are looking at two different removal mechanisms, and a professional can help design one system that handles each. For the uranium side of that problem, see how to remove uranium from water.

Whichever route you choose, treatment is not the finish line. Ion exchange resin saturates and RO membranes lose rejection as they age, with no visible sign that performance has slipped. The only way to separate a working system from a useless one is a post-treatment lab test, repeated on a schedule. Test before you treat to size the system, and test after to confirm it is actually holding your radium below the EPA limit.

Test your water before choosing treatment, since source water varies by region and by well.

Sources:

EPA National Primary Drinking Water Regulations, Radionuclides Rule (combined radium-226/228 MCL 5 pCi/L, gross alpha particle MCL 15 pCi/L, uranium MCL 30 ug/L): https://www.epa.gov/dwreginfo/radionuclides-rule
EPA Natural Radionuclides in Private Wells: https://www.epa.gov/radtown/natural-radionuclides-private-wells
EPA National Primary Drinking Water Regulations: https://www.epa.gov/ground-water-and-drinking-water/national-primary-drinking-water-regulations
USGS Water Resources, occurrence of radium in groundwater: https://www.usgs.gov/mission-areas/water-resources

Health disclaimer: WaterAnswer.com provides general information only. Radium is a known carcinogen. For guidance on testing and treatment specific to your home, contact your state health department or a certified water professional.