Risk assessment of radioactivity in water intended for human consumption in mainland Portugal

The requirements for radiological protection regarding radioactive substances in water intended for human consumption are established in the Council Directive 2013/51/EURATOM of 22 October 2013. In Portugal, the Directive was transposed to the Decree-Law 152/2017, of December 7, which states that the entities managing water supply must establish a quality control program based on a risk assessment. The risk assessment must consider the results of previous monitoring programs of both groundwater and surface water sources and the results of radionuclides measured in raw water, among others. To aid the entities managing water supply, risk maps of radon (Rn-222), uranium (U-238 and U-234), radium (Ra-226) and polonium (Po-210) were developed for mainland Portugal by the Laboratory of Natural Radioactivity of University of Coimbra using: (i) results from measurements performed in water samples retrieved from the database of the national regulation authority responsible for water and waste services (ERSAR); (ii) the terrestrial gamma dose rate map at the scale of 1:1 000 000; (iii) uranium concentration (n = 2681) and (iv) radium activity concentration (n = 609) measured in bedrock samples. ERSAR’s database comprises radon (n = 9473), gross alpha and beta (n = 10500), Po-210 (n = 1188), Ra-226 (n = 1143), U-234 (n = 1127) and U-238 (n = 1129) results from 5874 distinct groundwater and surface water sources. In this work, data are presented, methods and challenges for risk mapping of radon and terrestrial radionuclides in water samples are discussed.