The legal limit for radium in US drinking water has not changed since 1976. And it was not set based on what level is safe. It was set based on what it cost to remove radium at the time the standard was written.
Radium is a naturally occurring radioactive element found in tap water across all 50 US states. It is colourless, odourless, and tasteless — completely undetectable without specialist testing. A 2018 EWG analysis found it in the water supplies of over 170 million Americans. The EPA’s own estimate is that one in every 10,000 people drinking water at the current legal limit will develop cancer over a lifetime of consumption. Your water company is legally compliant. That does not mean your water is safe.
What Is Radium and How Does It Get Into Drinking Water?
Radium is a naturally occurring radioactive element — atomic number 88 — that forms as part of the uranium and thorium decay chains in rock and soil. As uranium and thorium in geological formations decay over millions of years, radium is one of the intermediate decay products produced. It dissolves into groundwater that passes through or sits in contact with radium-bearing rock formations, and from there enters water supplies — both municipal systems drawing from groundwater and private wells.
Unlike many water contaminants that enter supplies through industrial activity or agricultural runoff, radium contamination is primarily geological. It is not a pollution problem in the conventional sense. It is a natural feature of the geology underlying large parts of the United States — particularly the Midwest, Texas, the Great Plains, and parts of New England — that has always been present in groundwater and that has come into contact with human water supplies as those supplies have drawn increasingly from deep groundwater sources.
The two most common isotopes in drinking water are radium-226 and radium-228. Both are radioactive. Both emit ionising radiation as they decay. And both are classified as known human carcinogens.
Is Radium in Tap Water Dangerous?
Yes. Radium is classified as a Group A known human carcinogen by both the EPA and the International Agency for Research on Cancer — the highest carcinogen classification, reserved for substances with sufficient evidence of cancer causation in humans. This classification is not contested. The question is not whether radium causes cancer. The question is what level of radium in drinking water represents an acceptable cancer risk — and whether the current legal limit answers that question adequately.
The EPA’s own risk assessment for radium at the current maximum contaminant level estimates that one in every 10,000 people who drink water at that limit for a lifetime will develop cancer as a result. This is not an independent or adversarial estimate. It is the EPA’s own calculation, published in its regulatory documentation. One in 10,000 is the agency’s own number for the cancer risk it has decided is legally permissible.
To put that in context: the EPA typically uses a one-in-one-million cancer risk as the threshold below which a chemical in water is considered to pose negligible risk. The current radium limit is associated with a risk 100 times higher than that threshold. The EPA knows this. It set the limit anyway — because removing radium to the level that would achieve a one-in-a-million risk was considered too expensive in 1976.
Why Was the 1976 Legal Limit Based on Cost, Not Safety?
The EPA’s maximum contaminant level for radium — 5 picocuries per litre for combined radium-226 and radium-228 — was set in 1976 under the Safe Drinking Water Act. The standard was derived not from a risk assessment that calculated what level would be safe, but from a technical feasibility assessment that calculated what level water utilities could achieve using the treatment technology available at the time, at a cost considered economically reasonable.
This is a common feature of early Safe Drinking Water Act standards. The regulatory philosophy in the 1970s prioritised what was achievable over what was safe, partly because the cancer risk data for many contaminants was incomplete and partly because the cost of treatment was a significant political constraint. The result was a set of standards that were never designed to eliminate cancer risk — only to reduce it to a level achievable with available technology at acceptable cost.
The technology for removing radium from water has improved significantly since 1976. Treatment methods that were expensive or unavailable in 1976 are now standard in water treatment practice. The scientific understanding of radium’s carcinogenicity has also been substantially refined in the intervening 50 years. Neither development has been reflected in an update to the legal limit. The 1976 standard, based on 1976 technology costs and 1976 science, remains the enforceable federal maximum contaminant level in 2026.
How Does Radium Affect the Human Body?
Radium’s biological behaviour is what makes it particularly hazardous. It is chemically similar to calcium — the two elements are in the same group of the periodic table and share similar ionic properties. The body cannot distinguish between radium and calcium in the digestive and metabolic processes that regulate calcium absorption and distribution. When radium is ingested in drinking water, it is absorbed from the gut through the same mechanisms that absorb dietary calcium and directed to the same biological destination: bone tissue.
Once deposited in bone, radium does not leave easily. It has a long biological half-life in skeletal tissue. And while it is in bone, it emits ionising radiation — alpha particles and gamma rays — that irradiate the surrounding bone cells, bone marrow, and soft tissue at close range. This close-range, sustained irradiation is what drives the carcinogenic effect. The primary cancer associations are bone cancer and leukaemia, along with other cancers of tissues adjacent to bone.
The historical evidence for radium’s bone cancer effect is not abstract. The Radium Girls — factory workers in the early 20th century who painted watch dials with radium-based luminous paint and were instructed to point their brushes with their lips — developed devastating bone cancers and jaw necrosis from radium accumulation in their skeletal tissue. Their cases provided some of the earliest direct human evidence of radium’s carcinogenic effect and contributed to the development of radiation protection standards. The mechanism is the same when radium enters via drinking water, though at lower doses over longer timescales.
How Many Americans Have Radium in Their Tap Water?
A 2018 EWG analysis of water utility testing data found radium in the tap water supplies of all 50 US states, affecting more than 170 million Americans. The contamination is not confined to a specific region or geology — though the highest concentrations tend to occur in the Midwest, Texas, the Great Plains, and parts of New England where radium-bearing geological formations are most prevalent.
The EWG analysis also found that many water systems were reporting radium at levels above the health guideline derived from a one-in-one-million cancer risk threshold — meaning they were legally compliant with the 1976 standard while exceeding the level at which the EWG and many health researchers consider risk to be negligible. Legal compliance and health protection are, again, not the same thing.
Private wells are unmonitored for radium. The federal standard applies only to public water systems. In geological areas where radium is prevalent in groundwater, private well owners may be consuming radium at concentrations significantly above the already inadequate public system limit, with no regulatory requirement to test and no notification obligation.
Legally Compliant Does Not Mean Safe
This is the through-line of the radium story — and of the water quality conversation more broadly. A standard set in 1976 based on what treatment cost at the time, not on what level is safe, remains the legal limit in 2026. The EPA knows the limit is associated with a one-in-10,000 lifetime cancer risk. It acknowledges that this is 100 times higher than its own standard threshold for negligible risk. And the limit has not changed.
Water utilities that meet the 1976 radium standard are operating lawfully. Their annual water quality reports will show compliance. Nothing in those reports will tell you that the EPA estimates your lifetime cancer risk from the radium in that compliant water at one in 10,000. The information is in the regulatory documentation if you know where to look. It is not in the information your water company sends you.
Do you know what’s actually in your water?
The free Code of Hydration quiz takes 3 minutes and gives you a personalised score based on your specific habits, symptoms, and water quality — not just how much you drink.
How to Remove Radium From Drinking Water
Radium removal requires specific treatment approaches. Not all filtration methods are effective.
- Reverse osmosis is the most effective and widely available residential option for radium removal, typically achieving reductions of 85–95%. It removes radium alongside a broad range of other contaminants including PFAS, arsenic, nitrates, and chromium-6. For households in high-radium areas, reverse osmosis is the standard recommendation.
- Ion exchange (water softeners) using cation exchange resin are effective at removing radium because radium behaves like calcium and is captured by the same ion exchange process that removes calcium hardness. A properly maintained water softener in a high-radium area provides meaningful radium reduction alongside hardness removal.
- Activated carbon filters — including standard pitcher filters and most under-sink carbon units — do not remove radium. Radium is a dissolved metallic ion, not an organic compound, and does not bind to activated carbon. Standard filters provide no protection against radioactive contaminants.
- Check the EWG database. The EWG tap water database at ewg.org/tapwater allows you to search by zip code to see radium levels in your municipal supply relative to both the federal limit and the EWG health guideline.
- Private well owners must test independently. There is no regulatory requirement for private wells to test for radium. In geological areas where radium is prevalent, annual testing by a certified laboratory is the only way to know your exposure level.
Frequently Asked Questions
Is radium in tap water dangerous?
Yes. Radium is a Group A known human carcinogen classified by both the EPA and the IARC. The EPA’s own estimate is that one in 10,000 people drinking water at the current legal limit for a lifetime will develop cancer as a result — a risk 100 times higher than the EPA’s standard negligible risk threshold. A 2018 EWG analysis found radium in the water supplies of 170 million Americans.
Why hasn’t the radium limit been updated since 1976?
The 1976 standard was set based on what treatment technology could achieve at acceptable cost, not on what level is safe. Despite significant improvements in treatment technology and cancer risk science since 1976, the EPA has not updated the standard. The regulatory process for revising drinking water standards is slow and subject to economic and political pressures that have repeatedly delayed updates to inadequate legacy limits.
How does radium get into drinking water?
Radium leaches naturally from uranium- and thorium-bearing rock formations into groundwater over geological timescales. It is not primarily an industrial contamination problem — it is a geological feature of large parts of the United States, particularly the Midwest, Texas, the Great Plains, and parts of New England.
What does radium do to the body?
Radium behaves like calcium in the body and is absorbed from the gut and deposited in bone tissue. Once in bone, it emits ionising radiation (alpha particles and gamma rays) that irradiates surrounding bone cells, bone marrow, and adjacent tissue over years. The primary cancer associations are bone cancer and leukaemia.
What states have the most radium in groundwater?
The highest documented radium concentrations in US groundwater occur in the Midwest (particularly Illinois, Wisconsin, Iowa, and Minnesota), Texas, parts of the Great Plains, and portions of New England. However, the 2018 EWG analysis found radium in water supplies in all 50 states — no region is exempt.
This article is for general informational purposes only and is not medical advice. Always consult a qualified healthcare professional if you have concerns about your health or water quality.
Leave a Reply