Replacement cartridge will fit any 20-inch big blue filter housing Greatly reduces the taste and smell of chlorine Filters out organic materials and sediments Enclosed in a 5-micron filter membrane Replace once every 12 months (depending on the quality of water supply) Activated carbon is treated or activated with oxygen to give it tiny holes and make it absorbent like a sponge. This solid block of porous carbon creates a chemical reaction when water passes through which absorbs chlorine and other organic materials. There is a 5-micron membrane surrounding the activated carbon block filter to trap any particles that may detach during the water filtration process.