The objective of the research described in this article was to partially bridge the gap between formation potentials in model systems, e.g., humic substances, and by-product concentrations likely to be encountered in finished waters. The chlorination by-products chosen for study were trihalomethanes, total organic halide, trichloroacetic acid, dichloroacetic acid, trichloro- acetone, and dichloroacetonitrile. By-product formation from colored raw waters was found to be similar to that observed for aquatic humic and fulvic acids. Alum coagulation of a moderately colored surface water resulted in the removal of 50-90 percent of all by-product precursors tested.