This part of ISO 17379 specifies a method for the determination of selenium. The method is applicable to drinking water, surface water, ground water and rain water. The application range of this standard is from 0,02 ìg/l to 100 ìg/l. Samples containing selenium at higher concentrations than the application range can be analysed following appropriate dilution [1]. The method is unlikely to detect organo-selenium compounds. The sensitivity of this method is dependent on the selected operating conditions. It is important to use high purity reagents in all cases with minimum levels of selenium. The concentration of the blank solution should be less than the lower level of interest.