To minimise the consumption of chemicals and to enhance the flux, experiments have been carried out with a combined air/water cleaning at the water treatment facility Spannenburg (Water Supply Company Friesland, WLF). A pilot investigation was carried out on the recovery of filter backwash water. WLF has taken a full scale ultrafiltration plant (150 m3/h) in production in February 1999 in which the membrane elements are placed in a vertical position. The elements are periodically cleaned with a combined air/water wash. The Water Supply Companies Friesland (WLF), Oost-Brabant (WOB) and DHV Water have developed a new pressure vessel and interconnector for nanofiltration and ultra low pressure reverse osmosis plants. Using this new pressure vessel design, a 15% saving on membrane surface can be obtained without extra costs for pressure vessels. Includes 10 references, figures.