AO Smith Replacement Filter Cartridges
AO Smith AO-US-200 replacement cartridge (AO-US-200-F, $25--$35, 6-month / 600-gallon life): available at Lowe's and Amazon. AO Smith whole-home filter cartridge (AO-WH-300-F or AO-WH-200-F depending on model, $30--$50, 3--6 month life): at Lowe's. AO Smith RO filters (annual kit, $50--$75 excluding membrane): at Lowe's online and in-store. AO Smith's Lowe's distribution ensures consistent in-store availability for replacement parts without online ordering -- a practical advantage for households in markets with strong Lowe's penetration. Annual replacement costs: under-sink 3-stage ($60--$80), whole-home ($100--$200), RO ($60--$100 excluding membrane).