Normalization of permeate flux data is widely used to characterize membrane fouling under different experimental conditions. The main intention of normalization is to allow a fair comparison of feed water fouling potentials by eliminating the effects of different operational parameters used in the experiments, such as net driving pressure and clean-membrane resistance. However, it was demonstrated that the commonly used intuitive normalization methods usually could not serve their intended purpose. In this study, a new normalization method was proposed for characterizing water-fouling potential based on fundamental principles of membrane fouling. The intention of this normalization method was to define a fouling potential for feed water that was independent of, or at least, not strongly affected by operational conditions. Laboratory-scale ultrafiltration fouling tests were conducted under different colloid sizes, concentrations, and driving pressures. The experiments showed that the fouling potentials defined by the newly proposed normalization method were linearly related to the colloid concentration of the feed water and that the effect of operational conditions used in the fouling experiments on the fouling potential was minimal. (C) 2004 Elsevier Inc. All rights reserved.