Information on the effect of water quality on membrane cleaning is of vital importance as it gives industry the potential to lower the costs involved in membrane cleaning. The effect of the presence of sodium, calciurn, magnesium, iron(III), chloride and nitrate ions in water has been investigated for surface removal of reconstituted whey protein concentration from a 10 kDa polysulphone membrane using CTAB. The concentration of the ions present in the cleaning water, the ionic strength, the valence of the cations and the ionic activity were all important factors influencing the efficiency of removal of foulant from the membrane surface. In particular, at high ionic strength, the Surface removal efficieney decreased with the valence of the cation present in the water, but increased with ionic activity. Surface removal efficiency is reduced when ions interfere with the ability of the CTAB to disrupt the protein foulant layer by electrostatic repulsion. (c) 2004 Elsevier B.V.. All rights reserved.