Pentair OMNIFilter PB55-20 Carbon Water Filter, 20-Inch, Whole House Premium Heavy Duty Carbon Block Lead Reduction Replacement Cartridge, 20" x 4.5", 0.5 Micron. Premium Carbon Block Filter designed to protect your family from Lead and Cysts at every tap in your home for safer, better-tasting water. Fits All 20" Heavy Duty Housing and can replace any 20" x 4.5" carbon filter cartridge. Unique CARTRIDGE DESIGN provides professional-level lead reduction with the highest flow rate and the lowest pressure drop available in the industry. NSF INTERNATIONAL STANDARD 53 CERTIFIED for the reduction of Lead and Cysts when used in the Pentair OMNIFilter BF35-S-S18 filter housing or PB35-S-S18 filter system. 40,000 GALLON CAPACITY. Replace every 4-5 months or when you notice a drop in water pressure or water quality.