Radium and Uranium in Tap Water: Limits, Where They Occur, and How to Remove Them

Radium and uranium get into tap water naturally, as groundwater moves through rock and sediment that contain them. They are colorless, odorless and tasteless, so testing is the only way to know they are there. The EPA limits combined radium-226 and radium-228 to 5 picocuries per liter (pCi/L) and uranium to 30 micrograms per liter (µg/L). The concern is long-term: years of drinking water above these limits raises cancer risk, and uranium can also harm the kidneys. Ion exchange and reverse osmosis can remove both.

Here’s what the limits mean, where these contaminants turn up, and what to do if your water has them.

The federal limits

The EPA regulates radioactive contaminants, called radionuclides, under its Radionuclides Rule. The current version was published on December 7, 2000, updating standards that dated to the 1970s. The uranium limit took effect on December 8, 2003.

Contaminant	EPA limit (MCL)	Health goal (MCLG)	Health effects listed by EPA
Combined radium-226 and radium-228	5 pCi/L	Zero	Increased risk of cancer
Gross alpha (excluding radon and uranium)	15 pCi/L	Zero	Increased risk of cancer
Beta particles and photon emitters	4 millirem per year	Zero	Increased risk of cancer
Uranium	30 µg/L	Zero	Increased risk of cancer, kidney toxicity

A few terms worth knowing:

Picocuries per liter (pCi/L) measure radioactivity, not weight. That’s why radium is measured in pCi/L and uranium, which the EPA regulates partly for its chemical effects, is measured by weight in µg/L.
Gross alpha is a broad measurement of alpha radiation in the water. The EPA’s 15 pCi/L gross alpha limit excludes radon and uranium, which are handled separately.
The health goal (MCLG) is zero for all of these. The enforceable limit is higher than the goal. The gap between the two is why some organizations publish stricter health guidelines than the EPA limit. Our posts on the gap between EWG and EPA and California’s public health goals explain those differences.

Health effects

Radium. The Illinois Department of Public Health explains that only a small share of swallowed radium is absorbed. What is absorbed behaves like calcium and settles mostly in bone, where its radiation can damage nearby cells. Illinois links long-term exposure to higher rates of bone, liver and breast cancer, and says studies of workers with high exposure found effects such as anemia, cataracts and fractured teeth.

Uranium. Uranium is unusual because it is both radioactive and chemically toxic. The EPA lists kidney toxicity as well as increased cancer risk for water above the limit, and its regulatory documents describe soluble uranium as a kidney toxin.

Perspective on the risk. The Minnesota Department of Health frames the risk this way: drinking water with radionuclides delivers very low doses of radiation, and the higher cancer risk comes from drinking such water every day for many years. This is not a contaminant that makes people sick after a glass or a week.

Showering and bathing. For radium, Illinois notes that alpha particles do not travel through skin, so the main concern is drinking and cooking, not washing.

Where radium and uranium occur

Both come from natural geology, so the pattern is regional. The Minnesota Department of Health notes that surface water generally does not contain radionuclides at levels of concern. Groundwater is where elevated levels show up.

Radium. A U.S. Geological Survey study of principal aquifers found that about 3 percent of sampled wells had combined radium above the 5 pCi/L limit. The highest concentrations were in two aquifer systems, where more than 20 percent of sampled wells met or exceeded the limit:

The Mid-Continent and Ozark Plateau Cambro-Ordovician aquifer system, which supplies public water to parts of Illinois, Iowa, Missouri, Michigan, Minnesota and Wisconsin, according to USGS.
The Northern Atlantic Coastal Plain aquifer system, which runs along the East Coast.

USGS identified three conditions linked to high radium: oxygen-poor water, acidic (low pH) water, and high dissolved solids. In Minnesota, the state health department says the highest source-water levels are in the Mount Simon-Hinckley and Jordan aquifers in the southeast part of the state.

Uranium. A USGS study of 1,105 wells sampled about a decade apart found 64 wells (6 percent) above the 30 µg/L limit, and all but one were in the arid West. Concentrations were low to undetectable in humid climates. Regional USGS studies in parts of California’s San Joaquin Valley and Mojave Desert, and in southwestern Montana, have found higher shares of wells above the limit.

These are mostly measurements of untreated groundwater. Public water systems that use these sources must treat or blend their water to meet the limits. Private wells have no such requirement.

What our data shows for public water systems

We checked the radionuclide records for the 1,000 utilities in our database (EPA ECHO compliance records, checked October 7, 2026; last 12 quarters).

18 utilities have an entry under the EPA’s radionuclides rule.
17 of those 18 are monitoring and reporting entries, meaning the system missed or was late on a required test or report. That is not a finding that radium or uranium was too high.
One is a health-based limit (MCL) entry: Waukesha Water Utility in Wisconsin, dated April 1, 2023, and listed as closed. Our data now shows Waukesha’s source as purchased surface water.

Separately, 15 utilities in our data list combined radium as a top concern because levels are above a health guideline that is stricter than the EPA’s limit. That is different from an EPA violation. A utility can meet the federal 5 pCi/L standard and still exceed a stricter, non-enforceable guideline.

A utility may have resolved issues since our data was pulled. Check its EPA report or its Consumer Confidence Report for current results. You can look up your system by ZIP code, and our methodology page explains how we weigh violations and health guidelines.

How to find out about your water

On a public water system: Radium, gross alpha and (for many systems) uranium results appear in your utility’s annual water quality report. Our guide on how to read your water quality report shows where to look. If your system uses only surface water, radionuclides are rarely a concern. If it uses groundwater, look for the numbers.

On a private well: Nobody tests your well but you. Illinois recommends that private well owners use the 5 pCi/L public water limit as a guideline for radium, and testing is the only way to know. If you live over one of the aquifers above, or in an area of the West with known uranium, ask your state health department or a state-certified lab about a radionuclide test. Our well water testing guide covers how to find a certified lab.

Treatment that works

The good news is that proven, widely available treatment exists.

For radium:

Ion exchange water softeners. The Minnesota Department of Health lists ion exchange softeners among home systems that can reduce some radionuclides. Illinois says ion exchange can often remove about 90 percent of radium along with hardness. Removal depends on the softener being regenerated and maintained properly.
Reverse osmosis. Both Minnesota and Illinois list reverse osmosis (RO) as effective for radium.

For uranium:

Reverse osmosis and anion exchange. An EPA-hosted technical presentation on radium and uranium removal lists both as effective point-of-use methods for uranium. Uranium usually behaves differently from radium in water, so a standard softener aimed at hardness should not be assumed to remove it. Check a device’s certified performance data for uranium specifically.

Practical trade-offs:

Sodium. Illinois notes that ion exchange softeners add sodium to treated water, which matters for people on low-sodium diets. RO does not add sodium.
One tap vs. the whole house. An under-sink or countertop RO system treats only the water you drink and cook with. Because the main radium concern is drinking and cooking rather than bathing, that is often enough.
Certification. Look for systems certified to NSF/ANSI 58 (reverse osmosis), and confirm on the product’s performance data sheet that radium or uranium reduction is specifically listed. Radium and uranium are separate claims: many RO units are certified for radium but not uranium, including the AquaTru countertop and Aquasana OptimH2O systems. If uranium is your concern, find a model whose listing names uranium. Our explainer on NSF certifications and our comparison of reverse osmosis vs. carbon filters can help.
Retest after installing. Test the treated water to confirm the system is working, and keep up with filter and membrane changes.

Bottom line

Radium and uranium are natural, regional groundwater contaminants. The health risk comes from years of drinking water above the EPA limits, not from short-term exposure. If you’re on a public system, your utility must test and treat, and your water quality report will show the results. If you have a private well in an affected area, a test is the only way to know, and ion exchange or reverse osmosis can bring levels down.