The U. S. Environmental Protection Agency (USEPA) regulates the concentration of radioactivity in public drinking water systems (i.e., those that are publicly- or privately-owned, serve at least 25 people or 15 service connections for at least 60 days per year). To protect public health, the USEPA has established maximum contaminant levels (MCLS) for several types of radioactive contaminants in drinking water (40 CFR 141). For combined radium (i.e., Ra-226/228) the MCL is five (5) picocuries per liter. For gross alpha activity, the MCL is 15 picocuries per liter. For uranium, it is 30 micrograms per liter.
For beta emitters, the MCL is a concentration which produces an annual radiation dose of four (4) millirem effective dose equivalent in one year (65 FR 76708). The MCLs are calculated assuming a two (2) liter per day water intake using the 168-hour maximum permissible concentration (MPC) listed in a 1963-vintage NBS Handbook that used a “critical organ” philosophy (i.e., NBS Handbook 69).
The following is a listing of the derived concentrations of beta and photon emitters in drinking water, units of picocuries per liter (pCi/l) that yields an effective dose equivalent of four (4) millirem based upon the NBS Handbook 69 factors. If multiple radionuclides are present, compliance should be demonstrated using the “unity rule”.