A back-washing arrangement for cleaning a water filter arrangement comprising a filter element having a semi-permeable filtration wall comprising a folded filter arranged in a zig-zag configuration between an inner perforated cylinder and an outer perforated cylinder and a chamber comprising a chamber inlet for unfiltered liquid , a chamber outlet for filtered liquid and a wall arranged to keep said unfiltered liquid and said filtered liquid separated, wherein said back-washing arrangement is arranged inside of said filter element, further said back-washing arrangement comprises: - an elongated and hollow body having a longitudinal extension; - a mechanism configured to drive said elongated body in a rotational and/or an axial movement; - a plurality of nozzles arranged in fluid communication with a cavity inside of said body, said plurality of nozzles projecting laterally from said body such that a distal end of each of said plurality of nozzles is arranged in close proximity to said inner perforated cylinder of said filter element of said filter arrangement , and at least one of said nozzles comprises spring loading means for keeping said nozzle under spring load such that the distal end of said nozzle will follow the surface of said inner perforated cylinder while said back-washing arrangement is rotated; - an outlet arranged in fluid communication with said cavity of said elongated and hollow body; wherein said plurality of nozzles are arranged parallel to each other along a straight line on said body such that they project in the same direction, wherein each one of said first plurality of nozzles is arranged adjacent to at least another one of said plurality of nozzles , wherein the filter arrangement comprises a cap which covers the distal end of at least one of said plurality of nozzles . - an elongated and hollow body having a longitudinal extension; - a mechanism configured to drive said elongated body in a rotational and/or an axial movement; - a plurality of nozzles arranged in fluid communication with a cavity inside of said body, said plurality of nozzles projecting laterally from said body such that a distal end of each of said plurality of nozzles is arranged in close proximity to said inner perforated cylinder of said filter element of said filter arrangement , and at least one of said nozzles comprises spring loading means for keeping said nozzle under spring load such that the distal end of said nozzle will follow the surface of said inner perforated cylinder while said back-washing arrangement is rotated; - an outlet arranged in fluid communication with said cavity of said elongated and hollow body; wherein said plurality of nozzles are arranged parallel to each other along a straight line on said body such that they project in the same direction, wherein each one of said first plurality of nozzles is arranged adjacent to at least another one of said plurality of nozzles , wherein the filter arrangement comprises a cap which covers the distal end of at least one of said plurality of nozzles . wherein said plurality of nozzles are arranged parallel to each other along a straight line on said body such that they project in the same direction, wherein each one of said first plurality of nozzles is arranged adjacent to at least another one of said plurality of nozzles , wherein the filter arrangement comprises a cap which covers the distal end of at least one of said plurality of nozzles . <EOS>