Natural radioactivity of drinking water in Finland.

The mean annual effective dose from natural radionuclides for users of drilled wells was estimated to be 0.41 mSv, for users of wells dug in the ground 0.05 mSv and for people using water from waterworks 0.02 mSv. The highest effective dose from drinking water was caused by 222Rn (Fig. 2) constituting 75% and 60% of the total effective dose caused by all natural radionuclides for drilled-well users for users of wells dug in the ground, respectively. 210Po and 210Pb contributed the most to the effective dose caused by the longlived radionuclides. Contribution of the isotopes of radium (226Ra and 228Ra) to the total effective dose from drinking water was minor.