This document specifies a method to determine radium-226 (²²⁶Ra) activity concentration in all types of water by coprecipitation followed by gamma-ray spectrometry (see ISO 20042^[7]).

The method covers the measurement of soluble ²²⁶Ra activity concentrations greater than 0,002 Bq·l⁻¹ using a sample volume of up to 100 l of any water type.

For water samples with a volume of less than a volume of 1 l, direct gamma-ray spectrometry can be performed following ISO 10703 but with a higher detection limit. The typical detection limit for samples of 1 l to 5 l is in the range of 0,002 to 0,000 40 Bq·l^−1[8].

NOTE            This test method can be adapted to determine other naturally occurring isotopes of radium, such as ²²³Ra, ²²⁴Ra and ²²⁸Ra, if the respective ingrowth periods are taken into account.