In ultra-filtration or micro-filtration plants the commonly used method for fouling characterisation is based on an analysis of easily measurable process parameters such as membrane permeability. The results presented in this paper are included in a research project aiming to optimize membrane plant operation for drinking water production with a backwash procedure using air and water flow in dead-end ultra-filtration using inside-out hollow-fibres. Experiments on both semi-industrial and laboratory scale pilot plants were first performed with a clay suspension for different filtration conditions and backwash procedures. A comparison of backwash efficiency assessed by initial permeability recovery and by mass balances on particles was performed. From these experiments, it can be pointed out that: