222 Rn and 226 Ra Concentrations in Spring Water and Their Dose Assessment Due to Ingestion Intake

222 Rn and 226 Ra concentrations of less than a few to several thousands of Bq L − 1 have been observed in several underground bodies of water around the world. Although regulations for these concentrations in water have been implemented internationally, there are currently no regulations in place in Japan. However, concentrations that exceed these internationally recognized regulatory values have also been observed in Japan. In this study, concentrations in spring water in the northern part of Japan were measured and the effective dose from intake of the water was evaluated. 222 Rn concentrations were measured using a liquid scintillation counter, and 226 Ra concentrations were measured using a high purity germanium detector after chemical preparation. The measured 222 Rn concentrations (=12.7 ± 6.1 Bq L −1 ) and 226 Ra concentrations (<0.019–0.022 Bq L −1 ) did not exceed the reference values set by international and European/American organizations. A conservative estimate of the annual effective ingestion dose of 8 μSv for 222 Rn and 226 Ra obtained in this study is much smaller than the estimated overall annual effective dose of 2.2 mSv from natural radiation to the Japanese population. However, this dosage accounts for 8% of the WHO individual dosing criteria of 0.1 mSv/year for drinking water.