Microfiltration (MF) and ultrafiltration (UF) systems, as an alternative to conventional water treatment for drinking water, have been developed very fast due to their ability for the removal of microbial pathogens, especially Cryptosporidium and Giardia. One of the most important tasks for the application of UF systems is to monitor membrane integrity during operation, detect and repair the defects because small defects could result in significant reduction of pathogen removal efficiency and consequently reduce UF membrane performance. The objective of this project is to develop a decision-aid tool for operators that gives them the integrity level of their plant without having to disconnect all the modules and indicates if the measured level puts in danger the plant effectiveness and so if he has to immediately repair or if he can differ the repairing. (C) 2009 Published by Elsevier B.V.