Frequent Questions

How does EPA sample drinking water for radionuclides?

More than 60 drinking water sampling locations reported results in the United States in 2016 as part of the RadNet monitoring network. Drinking water samples are typically collected four times a year from taps and are sent to the EPA’s National Analytical Radiation Environmental Laboratory (NAREL)  for analysis. Each of these samples is analyzed for tritium (H-3) One sample per year from each location is analyzed for iodine-131 (I-131).

An annual composite sample from each sampling location is analyzed for gross alpha and beta radiation. Any sample with elevated gross alpha radiation (greater than 2 pCi/L) will be analyzed for radium-226 (Ra-226), plutonium (Pu-238, Pu-239 Pu-240), and uranium (U-234, U-235, and U-238). If the radium-226 result is between 3 and 5 pCi/L, then the sample is analyzed for radium-228 (Ra-228). All of the annual composite samples are also analyzed for gamma-emitting radionuclides. Twenty-five percent (25%) of the annual composite samples are analyzed for strontium-90 (Sr-90), rotating locations so Sr-90 is analyzed for each location every four years.


For more information, visit RadNet

For more information about precipitation and drinking water sampling analysis, visit Envirofacts on

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