Amsterdam is building a new housing estate IJburg. It will house 45,000 residents. A dual water supply system, supplying drinking water and household water to the customers, appears to be an attractive alternative. Household water will be used for toilet flushing and for washing clothes. This concept has environmental advantages, while it is economically feasible. Household water will be produced from local surface water by a local production plant and must be sustainable. A treatment scheme, comprising coagulation-flotation-filtration and nanofiltration, complies with all the requirements. Direct nanofiltration with air flush may be an attractive alternative, provided that it results in a stable and robust operation. Direct nanofiltration with air flush will be compared with the originally system of coagulation/flotation followed by rapid filtration and spiral-wound nanofiltration. In a pilot plant research at Amsterdam Water Supply air flush nanofiltration was investigated in a 20 runs trial using IJ-Lake water with only a micro screen before the capillary nanofiltration. Quality and operational aspects of this system were investigated. From a membrane autopsy a lot of clay and organic fouling was found.