Product Description The 3M Whole House Standard Diameter Water Filter Drop-in Replacement Cartridge AP420 for the AP100 & standard and large diameter Stainless Steel Housing Series, is a good choice in water filtration. Protect your hot water heater from scale buildup while getting the clean and clear drinking water you want with a AP420 filter cartridge 2 pack. Reduces sediment1 and scale1 Average cartridge life: 6 months (incoming water quality may affect cartridge life) Proprietary polypropylene manufacturing process Grooved surface increases total surface area for longer cartridge life compared than non-grooved filter cartridges Rigid construction helps to eliminate sediment “unloading” due to variances in water pressure Materials are FDA CFR-21 compliant.