In a filter device and in a method for the periodic cleaning of a filter of a water treatment or sewage treatment plant, a rotating filter is arranged within its own separate filter chamber, the bottom of which is designed as following a contour of the rotating filter. The provision of an own separate filter chamber makes it possible for the rotating filter to be cleaned, without other parts of a filtering installation having to be taken out of operation, and without the rotating filter having to be dismantled and removed from the filter chamber. Therefore no lifting cranes or separate cleaning basins are necessary.