Abstract: A deep bed filter of the type comprising an upright vessel of particulate filter medium, inlet means at the top of the vessel for introduction of an aqueous stream to be filtered, outlet means at the bottom for removal of filtered liquid and means for backwashing the medium by an upward flow of liquid, has as the filter medium bone char and sand, the bone char being located substantially above the sand. The sand generally comprises a particulate mineral filter material selected from silica sand, fused alumina, garnet, zircon, ilmenite and glass.