The purpose of this study was to examine the effect of feed water quality and operational parameters on the efficiency of backwashing. In this study, a series of fouling experiments were first performed under various operating conditions. The primary operating parameters varied throughout the experiments were particle concentration, operating pressure and solution ionic strength. A theoretical model for flux decline due to cake formation was evaluated and utilized to determine the structure of the cake layer formed during fouling experiments. Following each fouling experiment, the membrane was backwashed in order to relate the backwash efficiency to both physical and chemical parameters. Finally, a theoretical value for the particle packing density of the cake layer calculated from the model was correlated to the backwash efficiency in order to elucidate the effect of cake structure on the efficiencies of backwashing. Includes 6 references, figures.