This paper discusses a study done to investigate the applicability of membrane treatment on bank-filtered water. Three runs were carried out: nanofiltration of conventionally-treated surface water; nanofiltration of bank-filtered water; and, nanofiltration of a blend of groundwater and bank-filtered water. The following parameters were analyzed: flux loss; rejection of dissolved solids; reduction of TOC and UV254 absorbance; examination of the inorganic deposits on the membrane surface after the runs; HPC (heterotrophic plate counts) and phospholipids on the membrane surface; and, type of organic material deposited on the membrane surface (pyrolysis-GC/MS). The experiments were carried out using a Filmtec NF 70 membrane in the rapid bench-scale membrane test system RBSMT (Allgeier and Summers, 1995) and in a pilot system supplied with a 4"x40" module. Based on these parameters, the performance of nanofiltration in treating bank-filtered water was assessed, the reference experiments with conventionally-treated surface water were the basis for the comparison of the results. The experiments demonstrate the influence of different pretreatment processes on the performance of nanofiltration.