The aim of this paper is to study the benefits of back-flush system on membrane fouling, as a function of different water mixtures. In particular three different waters have been prepared to analyse their effects on membrane: water 1 has been set up with calcium and magnesium ions; water 2 is characterized by a high microbial content; and water 3 combines both the presence of calcium and magnesium ions and high microbial content. Permeate flux values have been studied as a function of the transmembrane pressure, with and without back-flush system. Results showed that, in several conditions, this device allows to obtain higher permeate flux values and to decrease membrane fouling, giving great advantages on process. These benefits are very important: firstly they permit to decrease the number of membrane washing procedures, reducing the use of aggressive washing solutions that lowers membrane lifetime; and secondly they allow to reach higher process yields. (C) 2010 Elsevier B.V. All rights reserved.