The aim of this study was to evaluate the performance of four bacterial short-term genotoxicity assays (Salmonella/microsome assay, SOS Chromotest, Microscreen phage-induction assay, differential DNA repair test) that are widely used and/or have a promising potential for the genotoxicity testing of water samples. Twenty-three samples of different origins (drinking and bathing water, surface water, municipal and industrial wastewater, pulp mill effluents, groundwater, and landfill leachates) were tested in these assays. In total, 20 samples were genotoxic: 13 in the Salmonella/microsome assay, 13 in the SOS Chromotest, 8 in the Microscreen phage-induction assay, and 19 in the differential DNA repair test. Although the differential DNA repair test was the most sensitive system, positive results were obtained also with some of the negative control samples, and it had the least power to detect different genotoxic potencies. The Microscreen assay was the least sensitive system due to nonlinear results and sample toxicity. The Salmonella/Microsome assay and the SOS Chromotest were of equal sensitivity, but the variance of the results was higher in the Salmonella/microsome assay. As the Salmonella/microsome assay also lacks toxicity correction for routine applications and ordinarily utilizes two strains, the SOS Chromotest appears to be the most promising test system for routine screening of water samples. Based on the present experiments, the investigated water samples were ranked according to their genotoxic potency as follows: landfill leachates > effluents from pulp production > wastewater > surface water > contaminated groundwater ≃ drinking and bathing water > control samples. The rankings obtained with the individual test systems were generally in good agreement. In addition, we present data on the impact of water treatment methods (activated sludge treatment, UV disinfection) and of alternative technologies (ozone vs ClO2 pulp bleaching) on the genotoxicity of water samples.