Ninety eight pharmaceuticals and other organic compounds (POOCs) that were amended to samples of chlorinated drinking-water were extracted and analyzed 1, 3, 6, 8, and 10 days after amendment to determine whether the total chlorine residual reacted with the amended POOCs in drinking water in a time frame similar to the residence time of drinking water in a water distribution system. Results indicated that if all 98 were present in the finished drinking water from a drinking-water treatment plant using free chlorine at 1.2 mg/L as the distribution system disinfectant residual, 52 POOCs would be present in the drinking water after 10 days at approximately the same concentration as in the newly finished drinking water. Concentrations of 16 POOCs would be reduced by 32% to 92%, and 22 POOCs would react completely with residual chlorine within 24 h. Thus, the presence of free chlorine residual is an effective means for transforming some POOCs during distribution.