This article incorporates permeate flux and fouling data from a recently published integrated membrane system (IMS) pilot study as inputs to a model for estimating capital and operation and maintenance costs developed for plants at scales beyond current design experience. Nanofiltration (NF) costs attributable to variations in chemical cleaning intervals (resulting from changes in permeate flux and feedwater recovery) were estimated based on membrane fouling rates, associated cleaning intervals, backwashing frequencies, permeate fluxes, and feedwater recoveries observed at pilot scale. Costs of integrated membrane systems using microfiltration (MF), ultrafiltration (UF), and conventional treatment to treat surface water prior to NF were compared. Costs of large systems (>3.8 x 10^4 m^3/d [10 mgd]) were also estimated and compared with extrapolations from cost surveys of existing membrane installations. Results are discussed within the article. Includes 25 references, tables, figures.