About 240 US public water systems logged a combined-radium violation starting in 2024 or later in EPA SDWIS records, nearly all of them small systems. Radium-226 and radium-228 are naturally occurring radioactive isotopes that leach from bedrock into groundwater. Long-term exposure increases cancer risk, particularly bone cancer.
The EPA's radium limit for drinking water is 5 picocuries per liter (pCi/L), combining radium-226 and radium-228. That threshold was first set in 1976 and was kept when EPA updated its radionuclides rule in 2000. In KYE's copy of EPA's Safe Drinking Water Information System (SDWIS) violation records, 241 public water systems had a combined-radium violation (for exceeding the limit or for missed monitoring and reporting) that began in 2024 or later.
Radium is radioactive. It decays inside your body. And because it mimics calcium, it accumulates in bone tissue, where it can cause cancer decades later.
Most of the affected systems are small: 223 of those 241 serve fewer than 3,300 people, and the largest serves about 17,000. Small towns and subdivisions on deep wells carry most of the radium problem.
Radium-226 and radium-228 are naturally occurring radioactive elements found in granite, shale, and phosphate rock. When groundwater flows through these formations, it dissolves trace amounts of radium. The deeper the well, the longer the contact time, the higher the radium.
In a national USGS study of 1,270 untreated well-water samples (Szabo and colleagues, 2012), every sample above the 5 pCi/L limit came from seven aquifer systems:
Surface water sources (rivers, lakes) typically have low radium. But groundwater-dependent systems – especially small towns with deep wells – face the highest risk.
Radium has a half-life of 1,600 years (radium-226) and 5.75 years (radium-228). Once it's in your water, it doesn't break down quickly. Treatment is expensive. Many small systems can't afford it.
The EPA set the Maximum Contaminant Level (MCL) for combined radium at 5 pCi/L in 1976 under the Safe Drinking Water Act. The health goal (MCLG) for radionuclides is zero, because any radiation dose carries some cancer risk.
But the rule has gaps. Systems with consistently low results can test as rarely as once every 3, 6, or 9 years. Radium levels can vary, especially in systems that blend multiple wells. A single test every 6 years might miss a change.
In KYE's copy of EPA SDWIS violation records, 241 public water systems had a combined-radium violation beginning in 2024 or later. The records mix limit exceedances with monitoring and reporting failures, so not every one means radium above 5 pCi/L, but each means the system's radium status needs attention.
The science on low-dose radiation has evolved since 1976. The limit hasn't.
Here are the states with the most public water systems logging a combined-radium violation that began in 2024 or later, from KYE's copy of EPA SDWIS violation records (which may be incomplete for some states):
| State | Systems with a radium violation since 2024 | Largest system affected (people served) | |------|-------|-------------------| | Colorado | 61 | about 7,600 | | Arkansas | 31 | about 13,000 | | South Dakota | 27 | about 1,400 | | Wisconsin | 25 | about 1,800 | | Indiana | 15 | about 16,100 | | New York | 13 | about 1,500 | | Virginia | 11 | about 8,500 | | Missouri | 10 | about 1,800 | | West Virginia | 8 | about 2,200 | | Kentucky | 7 | about 5,300 |
The pattern is clear: radium problems cluster in small groundwater systems, often in regions where wells tap aquifers with radium-bearing rock, like the Cambrian-Ordovician sandstones and dolomites of the upper Midwest.
In the USGS national survey, the highest combined radium measured was 20.4 pCi/L, about four times the legal limit, in a well in the North Atlantic Coastal Plain aquifer system. Overall, 4% of the samples tested for both isotopes exceeded 5 pCi/L.
Small systems have the hardest time fixing the problem. Treatment that removes radium (ion exchange, lime softening, or reverse osmosis) can cost a small town millions, and those costs fall on a few hundred or a few thousand households.
Radium is an alpha emitter. When ingested, it mimics calcium and gets incorporated into bone and teeth. Once there, it irradiates surrounding tissue for years.
EPA says long-term exposure to radium in drinking water increases cancer risk, and studies of highly exposed groups have linked radium to:
The latency period can run for decades. You won't feel sick today. The damage accumulates silently.
Children may be more vulnerable. Their bones are growing, which means more calcium turnover and more radium uptake. Studies of the 1920s radium dial painters (women who ingested radium while licking paintbrushes to a fine point) found high rates of bone cancer and head sinus cancers among the most heavily exposed.
The EPA's 5 pCi/L limit is based on a lifetime of drinking the water. Drinking water at several times the limit for decades raises that risk further.
If your water tests near or above the limit, point-of-use reverse osmosis is the usual household fix; RO systems certified for radium reduction remove most of it. Some households choose treatment even below 5 pCi/L, since the health goal is zero. Worth the investment. Check the water filter guide for systems tested specifically for radioactive contaminants.
If your water system has a radium violation or you suspect high radium, here's what to do:
And if you want to check whether your ZIP code has radium issues, use our free water quality lookup tool – it pulls EPA data for PFAS, lead, and radioactive contaminants by location.
Probably not all of it. Systems with low past results may test only every 3-9 years, and radium levels can change when utilities switch wells or change pumping rates. A single test in 2021 doesn't tell you what the levels were in 2023 or 2024.
Untreated groundwater data shows how common radium is at the source. In the USGS national survey of 1,270 well samples, about 4% of samples tested for both isotopes exceeded 5 pCi/L before any treatment, and the rate was highest in the Midcontinent and Ozark Plateau Cambrian-Ordovician aquifers. Private wells drawing from these aquifers are not covered by federal testing at all.
Another blind spot: small systems. They have fewer resources for treatment and data management, and many of the violations in SDWIS are monitoring and reporting failures, which means the actual radium level is unknown. For now, assume the data understates the problem.
How does radium compare to PFAS or lead in drinking water for public health risk? It's hard to rank, but here's context:
The point: radium doesn't get the same headlines as PFAS, but if your city is at 15 pCi/L, it's one of the most serious contaminant exposures you can have. Don't ignore it because it's not trending.
What is the safe level of radium in drinking water? The EPA's legal limit is 5 pCi/L for combined radium-226 and radium-228. However, no level of radiation exposure is technically "safe" – all radiation carries some cancer risk. The 5 pCi/L standard represents an acceptable risk level set in 1976. Some health advocates argue it should be lower.
How do I know if my tap water has radium? Check your water utility's annual Consumer Confidence Report (CCR), available on their website or by request. Look for "radium-226," "radium-228," or "combined radium." If you're on a private well, you need to test it yourself – contact your state environmental lab or a certified private lab. Testing typically costs $50-$100.
Does boiling water remove radium? No. Boiling concentrates radium by evaporating water. Never boil water to remove radioactive contaminants. Use reverse osmosis, distillation, or ion exchange treatment instead.
Which water filters remove radium? Reverse osmosis (RO) systems remove 95-98% of radium. Distillation units also work. Cation-exchange water softeners can also remove much of the radium, and EPA lists ion exchange among its best available treatments for radium. Activated carbon filters, Brita pitchers, and fridge filters do NOT remove radium. If you're above the EPA limit, invest in a certified RO system.
Why is radium so high in the Midwest? The upper Midwest sits on top of the Cambrian-Ordovician aquifer system, which includes radium-rich sandstone and dolomite formations. Deep wells drilled into these layers pick up radium as groundwater dissolves the rock. Surface water sources in the same region have much lower radium because the contact time with bedrock is shorter.