A nanofiltration membrane pilot plant was operated for one year at the Daytona Beach, Fla., Brennan water treatment plant. During that year, the pilot plant was evaluated for disinfection byproduct control and water production. This article discusses selection of the membranes and the quality of the water they produced, along with cost estimates for a 10-mgd groundwater nanofiltration plant. Includes 13 references, tables, figures.