The Cincinnati Water Works recently completed a yearlong demonstration study in order to develop a comprehensive overall plan for potential short- and long-term improvements needed at the Richard Miller Treatment Plant (RMTP), capacity 220 MGD. One of the main objectives of the demonstration study was to evaluate the feasibility for substitution of one or more of the existing treatment processes upstream of granular activated carbon filters by microfiltration (MF). One important facet of the study was the evaluation of alternate unit processes, which included the use of membranes. A MF membrane system was operated for 12-months of pilot-scale testing over four seasons. The feedwater to the MF pilot-scale system was Ohio River water that had been treated with alum and polymer, followed by tapered flocculation and a sedimentation process of lamella plate-settlers. The feedwater is of consistent water quality, due to additional settling time within two large open reservoirs that are located directly after the lamella plate-settlers. Following filtration, the full-scale plant is equipped with granular activated carbon (GAC) adsorption to remove synthetic and natural organics. Final treatment steps at the RMTP are fluoridation, pH adjustment and disinfection. The MF pilot testing was conducted from July 31, 1997 to July 31, 1998. A Memcor membrane unit was installed at the RMTP, equipped with two, 15-square meter (total of 323 ft[2]) membrane modules. The MF pilot-scale unit was capable of treating a range of flows between approximately 15-25 gpm. The pilot-scale study investigated removal capabilities for turbidity and solids, comparing the use of MF versus the conventional filtration processes. Includes 2 references, figures.