Changes in water quality from source water to finished water and tap water at two conventional drinking water treatment plants (DWTPs) were monitored.Beside the routine water quality testing,Caenorhabditis elegans-based toxidty assays and the fluorescence excitation-emission matrices technique were also applied.Both DWTPs supplied drinking water that met govment standards.Under current test conditions,both the investigated finished water and tap water samples exhibited stronger lethal,genotoxic and reprotoxic potential than the relative source water sample,and the tap water sample was more lethal but tended to be less genotoxic than the corresponding finished water sample.Meanwhile,the nearly complete removal of tryptophan-like substances and newly generated tyrosine-like substances were observed after the treatment of drinking water,and humic-like substances were identified in the tap water.Based on these findings,toxic pollutants,including genotoxic/ reproductive toxicants,are produced in the drinking water treatment and/or distribution processes.Moreover,further studies are needed to clarify the potentially important roles of tyrosine-like and humic-like substances in mediating drinking water toxicity and to identify the potential sources of these contaminants.Additionally,tryptophan-like fluorescence may be adopted as a useful parameter to monitor the treatment performance of DWTPs.Our obsenvations provided insights into the importance of utilizing biotoxicity assays and fluorescence spectroscopy as tools to complement the routine evaluation of drinking water.