This International Standard specifies a method for the determination of the genotoxic potential of water and waste water using the bacterial strains Salmonella enterica subsp. enterica serotype Typhimurium TA 98 and TA 100 in a fluctuation assay. This combination of strains is able to measure the genotoxicity of chemicals that induce point mutations (base pair substitutions and frameshift mutations) in genes coding for enzymes that are involved in the biosynthesis of the amino acid, histidine. NOTE 1 ISO 13829[8] applies for the measurement of genotoxicity of samples containing DNA-crosslinking agents. This method is applicable to: — fresh water; — waste water; — aqueous extracts and leachates; — eluates of sediments (fresh water); — pore water; — aqueous solutions of single substances or of chemical mixtures; — drinking water. NOTE 2 When testing drinking water, extraction and pre-concentration of water samples can prove necessary.