EWG's Tap Water Database


Radium, combined (-226 & -228)

Cottonwood Mobile Home Park

Radium is a radioactive element that causes bone cancer and other cancers. It can occur naturally in groundwater, and oil and gas extraction activities such as hydraulic fracturing can elevate concentrations. Read More.

Radium releases radioactive particles that harm health in many ways, causing tumors in bone, lungs and other organs; leukemia; and skin and blood damage. Water utilities typically report radium amounts in picocuries per liter (pCi/L), which is a measure of radioactivity in water. The two most common forms of radium are radium-226 and radium-228. They may be reported separately or together.

Federal law allows up to 5 picocuries per liter of combined radium-226 and radium-228 in tap water. Research by the U.S. Geological Survey shows that in some regions of the country, such as the mid-continental region and North Atlantic coastal region, more than 20 percent of sampled wells have radium in levels exceeding the federal drinking water limit. And the legal limit does not equate safety: The EPA estimates that one in every 10,000 people drinking water containing radium at this level would develop cancer over a lifetime.

California set a public health goal much lower than the federal limit - 0.019 picocuries per liter of radium-226 and 0.05 picocuries per liter of radium-228, concentrations that are lower than the detection limit for most water tests.

Click here to read more on radiological contaminants.





Samples exceeding legal limit (MCL)


Samples exceeding
health guidelines

Testing results - average by year

YearAverage resultSamples takenDetectionsRange of results

pCi/L = picocuries per liter.

State and national drinking water standards and health guidelines

Health Guideline 0.05 pCi/L

The health guideline of 0.05 pCi/L for radium, combined (-226 & -228) was defined by the California Office of Environmental Health Hazard Assessment as . This health guideline protects against cancer.

pCi/L = picocuries per liter.

EPA Maximum Contaminant
Level (MCL) 5 pCi/L

The enforceable federal standard that defines the highest level of a contaminant allowed in drinking water.

pCi/L = picocuries per liter.

EPA Maximum Contaminant
Level Goal (MCLG)0 pCi/L

A non-enforceable federal health guideline. For cancer-causing chemicals, these health goals are typically set to zero.

pCi/L = picocuries per liter.

All test results

Date Lab ID Result