Abstract: A method of backwashing bundles of inside-skin tubular filter membranes in modules, in which:a circuit is provided so that dead-end mode filtering takes place with the tubular membranes being fed from one end while cross-flow mode filtering takes place with the tubular membranes being fed from the other end, thereby ensuring in both cases that the major portion of the matter stopped by the membranes collects in the same relatively small zone in the bundles of membranes contained in the modules;water is drawn off from the periphery of the modules; andbackwashing is performed in two stages: a first stage in which all of the backwashing water is used for cleaning said relatively small zone and in which the recirculation loop that enables cross-flow filtering to be performed is closed; and a second stage in which the backwashing water is caused to pass through all of the membranes and all the recirculation loop.Apparatus for implementing the method is also described and is shown in FIG.