Many organic contaminants in water supplies contain organically bound chlorine. The authors of this article evaluated the formation of purgeable and nonpurgeable organic chlorine as a function of the type and concentration of precursor material, the type and dosage of chlorine, pH, temperature, and ammonia concentration. Results indicate that the amount of organic chlorine formed increases with increasing chlorine dosage, increasing total organic carbon concentration, increasing temperature, and decreasing pH. Furthermore, the concentration of organic chlorine in a public water supply can be minimized by avoiding prechlorination and withdrawing water from a source with a low concentration of precursor material and a cool temperature. This article outlines the materials used by the authors, as well as analytical methods, experimental procedures, and detailed results. Includes 29 references, tables, figures.