EWG's Tap Water Database — 2021 UPDATE

picture of test tube and beaker in laboratory


November 2021


Radioactive elements enter groundwater from natural deposits in the earth’s crust and can also be found in higher concentrations when human activities such as uranium processing and disposal, mining, or gas and oil drilling or fracking unearth these elements from the rock and soil.

Radioactive elements produce the type of radiation called “ionizing” because it can release electrons from atoms and molecules and turn them into ions. Ionizing radiation damages DNA. Drinking water contaminated with radioactive substances increases the risk of cancer and may harm fetal development.

Is there a safe level for radiation in water?

The Environmental Protection Agency has classified all ionizing radiation as “known to cause cancer in humans” and has set a health guideline of zero for all radioactive elements in drinking water. But federal legal limits for radiation and radioactive contaminants are based on the cost and feasibility of removing the contaminants. They don’t always reflect the amount of exposure that the EPA and other public health agencies consider to be safe for human health.

Federal law requires water companies to monitor radioactivity levels in drinking water systems that serve more than 25 customers. EWG’s Tap Water Database reports that more than a dozen different radioactive elements are detected in American tap water. The most common are beryllium, radon, radium, strontium, tritium and uranium. Water systems sometimes screen for groups of radiation-emitting substances, and report total alpha or beta particle activity instead of individual substances.

EWG data show that radioactive contaminants are detected in water serving 165 million people across the U.S. There is clear evidence that high doses of radiation cause cancer in various organs. The probability of developing cancer decreases with lower doses of radiation but does not go away.

California has set public health goals for radium-226, radium-228 and uranium, and these values are 60 to 70 times lower than the federal legal limits. California’s public health goals are concentrations that pose a minimal risk of cancer, typically a one-in-a-million increase in lifetime risk of developing cancer.

Who is most at risk for radiation-related harm?

Different types of radioactive elements are associated with different health effects, and all of them increase the risk of cancer.

Recent research also finds that radioactive substances may damage the nervous, immune and endocrine systems.

As with many carcinogens, early life exposures to radioactive materials are more harmful than exposures to healthy adults. In 2002, Kirsten Moysich of the Roswell Park Cancer Institute, in Buffalo, reviewed epidemiological studies of the Chernobyl nuclear accident and found that children ages 5 and younger had elevated rates of thyroid cancer, compared to older children and adults.

The developing fetus is especially sensitive to the effects of ionizing radiation. At doses higher than those typically received in drinking water, radiation can impair fetal growth, cause birth defects and damage brain development. There is no evidence of a dose threshold below which a fetus would be safe from these effects. This means that even very small amounts of radioactive contaminants in tap water may pose a risk during pregnancy.

How to reduce people’s exposure to radioactivity in the environment

The last time the federal government took measures to reduce radioactivity in drinking water was in 2000, when, under a court-imposed deadline, the EPA published the Radionuclides Rule. The rule established a drinking water standard for uranium and required 795 water systems, most of them dependent on groundwater, to implement radiation treatment technology.

Other than the uranium water standard, the federal legal limits for non-radon radioactivity in drinking water have remained unchanged since they were first established in 1976. These include the standards for combined radium-226 and radium-228, as well as the limit for alpha particle and beta particle radioactivity.

As new research finds more information about the harm of radioactive substances, existing drinking water standards appear insufficient to protect people. Current detection limits for radioactive elements are greater than the health-based limits. Therefore, many people are told that their drinking water has no detectable radiation when, in fact, they face an elevated risk of developing cancer from the radioactivity present.

Americans whose water comes from systems serving fewer than 25 people, and those who drink well water, are not notified of the presence of radioactive compounds in their water.

The federal government needs to do much more to protect people from radioactive contaminants in water, by requiring more extensive radiation testing and better disclosure, and tightening the legal limits to bring them closer to the health goal of zero radiation in drinking water.

How can I find out about radioactivity in my water and home?

1. Find out whether there is any radioactivity measured in your drinking water.

Check EWG’s Tap Water Database. If your water provider is not listed, contact the utility for records of recent testing. If you drink well water, your county health department should be able to inform you if it detects radioactive elements in any wells in your area. Get your well water tested if there are indications of radioactivity in your region.

2. If radiation is detected in your water, consider buying a water filter.

Choose a water filter certified to remove the type of radioactivity present in your water. You will need a whole-house filter if your water contains radon or tritium, which can be released from shower or bath water and inhaled.

3. Check on radon.

If you live in a region with radon in soil or rock, you likely have greater exposure to radon from indoor air than from drinking water. A simple multiple-day air sampler kit can help you identify whether you have high levels of radon in your house. If you have radon in the house, consider installing a mitigation system in your basement or crawl space. The EPA’s radon program offers good advice about radon in indoor air.

Radioactive elements most commonly detected in drinking water

Element Primary health concern Detection level, in picocuries per liter* Health-based limits** (one-in-a-million cancer risk), in picocuries per liter unless noted National Maximum Contaminant Level (MCL), in picocuries per liter unless noted Cancer risk at legal limit
Radium-226 & -228 Bone cancer, other cancers 1 0.05 pCi/L# 5 pCi/L for combined radium 226+228 7 cancer cases per 100,000 exposed
Radon Lung cancer via inhalation 100 1.5 An advisory level of either 300 or 4,000##
Uranium Kidney damage, cancer 1 0.43 20### pCi/L 4.6 cancer cases in 100,000
Tritium Cancer 1,000 400 20,000 5 cancer cases in 100,000
Strontium-90 Bone cancer, leukemia 0.5 0.35 8 2 cancer cases per 100,000

Source: EWG, from California’s State Water Resources Control Board 2016 Groundwater Information Sheet on Radionuclides and the EPA’s 2012 Edition of the Drinking Water Standards and Health Advisories.

* Picocuries are a measure of the intensity of radioactivity of sample material. A unit of piC/L reflects the intensity of radioactivity in a liter of water.

** Since the detection limits for radioactive substances are greater than the health-based limits, even residents of communities with “no detected radiation” may face a risk of developing cancer from radioactivity in drinking water.

#Radium-226 is more commonly found in groundwater than radium-228. EWG applied the health guideline of 0.05 pCi/L for radium-226 to radium-226 and radium-228 combined. This approach is conservative, since the health guideline for radium-228 (0.019 pCi/L) is lower than the guideline for radium-226.

##There is no established requirement for radon monitoring in drinking water. The EPA has an advisory level for radon of 300 piC/L for tap water in states with no program to address radon risk in indoor air. For states such as California that are taking action to reduce radon levels in indoor air by developing an enhanced indoor air program, the EPA has an advisory level of 4,000 pCi/L for tap water. New Hampshire has an advisory level of 2,000 piC/L for tap water.

###The legal limit for uranium is set at 30 micrograms per liters (ug/L, equivalent to parts per billion), but utilities can also report uranium in picocuries per liter (pCi/L), which is a measure of radioactivity. EWG translated the MCL to pCi/L using a conversion factor developed by the EPA. With this conversion approach, the limit of 30 ug/L corresponds to 20 pCi/L. Multiple forms of uranium can be detected in water, including uranium-234, uranium-235 and uranium-238. Uranium-234 is far more toxic to human health, but not always analyzed in water.


California Office of Environmental Health Hazard Assessment (OEHHA). Public Health Goals (PHGs) Available at

California State Water Resources Control Board. Groundwater Information Sheet: Radionuclides. 2016. Available at

Environmental Protection Agency. 2012 Edition of the Drinking Water Standards and Health Advisories. EPA 822-S-12-001.

EPA. National Primary Drinking Water Regulations; Radionuclides; Final Rule Environmental Protection Agency. Dec. 7, 2000. 65 FR 76707.

EPA. Radiation Health Effects. Available at

EPA. Radon Program. Available at

EPA. National Primary Drinking Water Regulations. 2017. Available at

K.B. Moysich et al. Chernobyl-Related Ionising Radiation Exposure and Cancer Risk: An Epidemiological Review. Lancet Oncology 2002, 3(5):269–279.

B. Weinhold. Unknown Quantity: Regulating Radionuclides in Tap Water. Environmental Health Perspectives, 2012. Available at