Replacement Filter For The Basic Main Faucet Under Sink Water Filter System (AO-MF) - Easy replacement and no plumber necessary. Includes one Carbon Block filter. Does NOT fit AO-MF-ADV, AO-FF, or AO-MF-B filter systems. Purifies Water & Reduces 99% of 9 Harmful Contaminants - Basic filtration while leaving in all essential minerals. Reduces chlorine, lead, atrazine, lindane and turbidity. System will not reduce TDS. Long Lasting & Cost Efficient - No water is wasted and no harmful contaminants are added to your water during filtration. Filter lasts for 1,389 gallons or 6 months. Use only certified, genuine AO Smith replacement filters for continued contaminant removal and system performance. IAPMO Tested & Certified to NSF/ANSI standards 42 and 53.