Impurities such as particulates and some dissolved salts present in the water used for cleaning of a polysulphone ultrafiltration membrane have been found to affect the efficiency of the cleaning. A cationic surfactant, CTAB (cetyltrimethyl-ammonium bromide), was used for membrane cleaning after ultrafiltration of a 0.1 wt% reconstituted whey protein solution. Colloidal-free water used for cleaning was doped with a known amount of the ions : calcium, sodium, chloride, nitrate and sulphate. The presence of calcium in water, at the usual concentrations found in tap water, did not greatly affect cleaning efficiency while chloride was found to reduce cleaning efficiency. Sodium, nitrate and sulphate appeared to improve the flux recovery during membrane cleaning. The cleaning efficiency was also improved at higher ionic strengths. Calculations were carried out to demonstrate that the differences were statistically significant.