Researchers at the Denver Water Department's reuse demonstration plant in Denver, Colorado, found that the effectiveness of chlorine dioxide treatment is critically dependent on the performance of the generator. Because high chlorine dioxide yields can be obtained even when excessive concentrations of undesirable by-products are present, chlorine dioxide yield alone cannot be used as a measure of optimum generation conditions. It is necessary to monitor carefully all of the various chlorine species produced such as chlorite, chlorine, and chlorate, as well as chlorine dioxide. Includes 24 references, tables, figures.