New regulation on drinking water quality in the Province of Quebec in Canada, raised interest in nanofiltration (NF) technology for surface water treatment. Indeed, most of the surface waters of this province have a relatively low turbidity and are not very alkaline but contain significant amounts of natural organic matter (NOM) which makes them difficult to treat at a small scale with conventional treatments. NF allows simultaneous high removal of suspended matter, pathogens and NOM as long as the integrity of the system is maintained. It is rather simple to operate and very compact. NF is already used in Northern Europe under similar conditions, specially in Scotland and in Norway where more than one hundred plants have been built since 1990. But few data are available regarding performances of these systems, in particular about the critical question of membrane fouling. The main scope of this study was to address, on a pilot scale, the effect of the raw water quality and operating conditions (permeate flux, recovery rate, recirculation flow rate) on the fouling rate of a NF membrane. The project was carried out with raw water coming from the Saint-Charles River, in the area of Quebec City (Canada). Eighteen short pilot runs were conducted during summer and fall 2001. There was a good correlation between TOC and UV absorbance at 254 nm (UV254). The raw water specific UV absorbance (SUVA), based on TOC, was around 4.9 Lm-1mg-1. This indicates the importance of high molecular weight hydrophobic humic substances in the raw water. Includes 5 references, table, figures.