This International Standard specifies a method for the determination of the genotoxic potential of water and wastewater using the bacterial strains Salmonella typhimurium TA 100 and TA 98. This method includes sterile filtration of water and wastewater prior to the test. This International Standard is applicable only to the detection of genotoxic substances which are in the filtered aqueous phase. It is not applicable to the detection of genotoxic substances adsorbed by the retained particles.