In Luxembourg the largest drinking water production plant treating reservoir water with conventional technology including ozonation is in operation since 1969. Its maximum capacity is 64,000 m(3)/d. After 40 years of operation the need for both modernizing and extension of capacity to 100,000 m(3)/d emerged. Nowadays, due to new developments in technology and research it is possible to assess the water treatment processes more effectively with regard to current and future requirements. Against this background, membrane processes combined with conventional and advanced processes were identified as potential option and long term pilot-scale tests were started in June 2008. Different treatment process schemes all including membranes are investigated in a one year pilot plant period. Various treatment steps such as different pre- and post-treatment steps, various membranes and membrane materials and also conventional treatment steps are compared and assessed. (C) 2009 Elsevier B.V. All rights reserved.