Big Blue Water Filter Replacement Pack, 20 Inch (5 Micron PP, Carbon Block & 1 Micron PP)Replacement cartridges will fit any 20 inch Big Blue water filter system Stage 1: Sediment filter (5 Micron), removes mud, rust, dirt, floating particulates or any other large particles Stage 2: Carbon block filter reduces fine sediment, chlorine taste and the concentration of heavy metals such as lead and copper Stage 3: Sediment filter (1 Micron), further removes contaminants, oils and up to 60% of bacteria