This article summarizes the research conducted by the East Bay Utility District (EBUD), Oakland, California, to optimize clay-polymer coagulation used in conjunction with direct, in-line filtration to treat low-turbidity waters. During 1982 and 1983, cationic polymers were used as the primary coagulants, with and without clay, for extended periods at three EBUD direct filtration plants. This article compares the effectiveness of polymer, clay-polymer, and alum coagulation and discusses advantages of each. Chemical costs, sludge production, and use of backwash water were compared for the three types of coagulants. Other aspects of polymer use including quality control, effect of age, chlorine demand, trihalomethane formation, and polymer residuals are discussed. Includes 4 references, tables, figures.