²²⁶Ra and ²²²Rn concentrations in different inland waters have been determined, for a number of years, at the Central Laboratory for Radiological Protection, mostly at the request of interested water users. The measurement method applied consisted, for ²²⁶Ra, in chemical separation of this element from 10-litre water sample and subsequent alpha counting of ²²²Rn + daughters, Rn being de-emanated from the concentrate into Lucas-type scintillation chambers. For ²²²Rn the method was similar (de-emanation and measurement only).
²²⁶Ra concentrations in surface waters, well and tap waters as well as those from geological boreholes, are presented and discussed. The typical ²²⁶Ra content in fresh waters is of the order of 1 to 10 mBq/dm³, although deep waters showing concentrations up to 330 mBq/dm³ have been found.
The daughter of the above, ²²²Rn, occurs in fresh waters in considerably higher concentrations, of the order of Bq/dm³. It indicates that its prevailing origin is other than by radioactive decay of ²²⁶Ra contained in water, namely by contact of water with surrounding rocks and soils where ²²²Rn accumulates.