The City of Appleton is in the process of implementing a new 24 mgd water treatment plant. The water supply is characterized by organic carbon concentration and severe taste and odor occurrences. Ultrafiltration (UF) and microfiltration (MF) were identified as candidate technologies to remove Cryptosporidium and other disinfectant pathogens while controlling disinfection byproduct formation. Low-pressure membrane filtration was chosen for further investigation as opposed to ozonation and biological filtration, and side-by-side pilot testing of four UF and MF systems was performed. The feasibility of UF or MF as a polishing treatment in lime softening plants was demonstrated, and a membrane system was preselected at bid, with award of bid contingent upon regulatory approval. Integration of the membrane system into the new softening plant presented several design challenges. Pilot testing showed incompatibility of the membrane system with even low concentrations of polymer, an issue which limits softener loading rate. The transmembrane pressure during pilot testing was sensitive to pH shifts, apparently either organic fouling at low pH and calcium carbonate scaling at high pH, leading to the need for more precise pH control than would have otherwise been required. The additional recycle water associated with membrane system bleed and backwash presents issues related to regulatory limits on backwash recycle and softener performance.