Groundwater is still one of the main sources for the production of drinking water. In the preparation of drinking water, the groundwater is first aerated and then filtered through a sand filter in order to remove Fe, Mn, NH4 and methane. After saturation, these sand filters have to be backwashed periodically. In the past, the backwash water was discharged in the sewage either directly or after sedimentation. However, the first pilot trials with ultrafiltration showed already in 1995 that this technique was very promising for the recovery of backwash water. As a result, the first full-scale ultrafiltration installation was built at the drinking water company NRE (Nutsbedrijf Regio Eindhoven, now WOE) in Eindhoven, Holland, in 1997. A Belgian drinking water company started in the beginning of 1998, in collaboration with Vito, with pilot testing on this subject. Long-term experiments were carried out at four different locations, with different water qualities. At one location the backwash water coming directly from the sand filters (bulk fraction) was filtered; at the other locations the supernatant, which is formed after sedimentation in a settler, was used as feed for the UF pilot. As a result of the sedimentation process, the Fe content is lower in the supernatant than in the bulk fraction. The experiments were done with two different membranes: X-Flow and Stork. Both membranes are operating in dead-end mode with a standard backwash procedure in a very reliable and stable way. Special attention was given to the optimization of the chemical cleaning procedure and the permeate quality in respect of colony forming units (CFU). At the last location, a set of short-term experiments was carried out in order to get more insight in the fouling behaviour of the backwash water. Therefore, different operation modes were compared (low-high fluxes, short-long filtration time), keeping the dirt load either constant or variable. These results will also be discussed in this paper.