Abstract. The determination of radium isotopes in drinking water by liquid scintillation technique requires some reagents that are used for separating radium from water samples. One of the main reagents is BaCl 2 ·H 2 O. This paper presents the study of this compound and shows that barium chloride reagent is naturally contaminated with 226 Ra. The 226Ra activity concentration in BaCl 2 ·H 2 O reagent produced by chemical companies from Poland and other countries is equal to a few dozen Bq/kg. Furthermore, 14 mL of 0.10 M BaCl 2 ·H 2 O solution is the optimum amount which should be used for the chemical procedure. At the optimum amount of barium chloride and 2-hour measurement, the detection limit of 226 Ra and 228 Ra of the liquid scintillation counting method is equal to 5 and 30 mBq per sample, respectively.