Abstract: A liquid filter device includes an upwardly open structure having a bottom and a floor positioned above the bottom, the bottom and the floor defining therebetween a chamber. A filter element comprising granular material is supported by the floor within the structure. Liquid to be treated passes downwardly through the granular material in contact with a gas passing upwardly through the granular material during a normal filtering and processing operation. During an operation for washing the granular material, water and gas pass upwardly through the granular material. A plurality of nozzles open into the granular material and have stems communicating with the chamber. The plurality of nozzles includes first nozzles having openings for, during the normal operation, passing liquid from the granular material into the chamber, and for, during the washing operation, distributing the water and gas from the chamber into the granular material.