Abstract: A composition and method for the bactericidal treatment of water with oligodynamic metal ions. The composition comprises a particulate silver yielding material and a particulate filler material which is intermixed with the silver yielding material. The silver yielding material comprises a highly porous carrier having a hardness which is greater than that of elemental silver and a layer of elemental silver on the surfaces of the carrier, and the filler material comprises a material, such as charcoal, having a hardness which is less than that of elemental silver. The composition is utilized in accordance with the method of the invention by passing a stream of water through a quantity of the composition to cause the particles of silver yielding material to mechanically interact with each other to release silver into the water.