In Nijmegen (The Netherlands) groundwater is withdrawn by NUON to produce drinking water (which is also used for industrial purposes). To be able to meet the future needs for water, NUON will need to find other sources, to prevent exceeding the limits given in the groundwater licenses. An opportunity could be the scenario in which Philips Semiconductors (a client of NUON with a considerable water use applied in the production of semiconductors) is supplied with treated surface water instead of treated groundwater (i.e. drinking water). To investigate the technical feasibility of this scenario a pilot investigation, using Zenon membrane, has been performed. Dosing air underneath the membranes has proven to be necessary to control fouling. To be able to judge the consequences for the ultrapure treatment plant of Philips (with which the supplied NUON drinking water is treated) a hyperfiltration installation was part of the pilot plant. Analysis afterwards showed mainly biological fouling on the HF membranes. It is expected that a more careful cleaning of the piping work before operation will substantially reduce this type of fouling. Based on the reliability and the constant quality of the treated water the conclusion has been drawn that the switch from treated groundwater to treated surface water is technically feasible.