For use in whole house water filtration systems that accept 20x4.5 inch cartridges, the FM-BB-20-1A Watts pleated water filter cartridges helps reduce up to 99% of harmful cysts, including Giardia and Cryptosporidium. Thanks to its pleated design, this cartridge is also highly effective at capturing sediment, limescale and dirt as small as one micron, ensuring your water is virtually free of these impurities. Replace every six months for best results. Order the FM-BB-20-1A Watts water filter cartridge your whole house system needs online from us today.