The selected materials in a filter that form the barrier to the passage of filterable suspended solids or dissolved molecules. Filter media are used to remove undesirable materials, tastes, and odors from a water supply and to adjust the pH in a water supply. Filter designs include: 1) loose media filters with grains, resin, or other particles lying in beds or loosely packed in column-form

in tank-type filters; or 2)cartridge-type filters which may contain membranes, fabric, fiber, bonded-ceramic, precoat, or cast solid-block filter media. The media used in some filters are chemically inert, such as sand, which performs only a mechanical filtration. Other filter media are multifunctional, chemically-reactive media such as calcite, activated carbon, magnesia, manganese dioxide, and manganese greensand.