Site-specific empirical models of trihalomethanes (THMs), haloacetic acids (HAAs), and the organic precursors of these compounds were developed based on pilot study data. Either chlorination by-product precursors or chlorination by-products themselves were treated as dependent variables, and either water quality parameters or process parameters comprised the independent variables. Ultraviolet absorbance was found to be the most effective conventional water quality parameter for predicting precursor removal in treatment processes. A first-order model was developed to predict the removal of THM and HAA precursors in waters treated with ozone and subsequent granular activated carbon filtration. In a separate analysis, haloacetic acid concentrations were predicted as a function of THM concentrations. Among other findings, these models have suggested a negative impact of filter aids on chlorination by-product precursor removal at a direct filtration plant.