Presently, a computer model developed with funding from the USEPA is being used in the regulatory development effort. The model estimates the removal of trihalomethane precursors by coagulation and predicts the formation of THMs upon chlorination of natural waters during drinking water treatment. In order to address concern regarding the applicability of the model to DBP Rule development, a bench-scale study was performed for the AWWA's Disinfectant/DBP Technical Advisory Workgroup (TAW), which was designed to produce data for future expansion, refinement and calibration of the model. The primary objectives of the bench-scale project were to: 1) Investigate the formation of DBPs upon ozonation of raw and settled waters, and 2) Determine the impact of coagulant type, coagulant dose and coagulation pH on the removal of THM and haloacetic acid (HAA) precursors material from natural waters. This paper presents an overview of the experimental results discussed in terms of the USEPA's risk level concentrations. Complete results of the study, "Effect of Coagulation and Ozonation on the Formation of Disinfection By-Products," are available through AWWA. The complete study is publication order number #55005.