ISO 13165-3:2016规定了通过共沉淀和伽马光谱法测定所有类型水中的镭-226（226Ra）活性浓度（见ISO 18589‑3）。 所述方法适用于使用1 l至100 l任何水类型的样品体积测定大于0.02 Bq l−1的可溶性226Ra活性浓度。 对于体积小于1升的水样，可按照ISO 10703进行直接伽马光谱测定，检测限更高。 注:本试验方法还允许测定镭的其他同位素223Ra、224Ra和228Ra。

ISO 13165-3:2016 specifies the determination of radium-226 (226Ra) activity concentration in all types of water by coprecipitation followed by gamma-spectrometry (see ISO 18589‑3). The method described is suitable for determination of soluble 226Ra activity concentrations greater than 0,02 Bq l−1 using a sample volume of 1 l to 100 l of any water type. For water samples smaller than a volume of 1 l, direct gamma-spectrometry can be performed following ISO 10703 with a higher detection limit. NOTE This test method also allows other isotopes of radium, 223Ra, 224Ra, and 228Ra, to be determined.