This article reports on two industrial water supplies in the North of the Netherlands. These projects are comparable with system design: ultrafiltration and reverse osmosis are used to produce process water with an extrememly low salt content from surface water. The only preliminary treatment upstream of the membrane system is continuous filtration with flocculant dosing. One complicating factor is the great variation in the quality of the surface water, which also depends on the season. Despite the limited number of experiments, the technical and financial feasibility were determined on the pilot scale and the main obstacles affecting ultrafiltration and reverse osmosis were determined. Includes 4 references, tables, figures.