Abstract: A water filter system having a housing for a plurality of serial-flow connected filter cartridges with distinct filtering characteristic related to the direction of flow of water being filtered. Each filter cartridge has a membrane wrapped activated carbon filter body. One of the filter bodies includes a heavy metal bacteriostat. The cartridges are each releasably retained in a manifold by keyed connectors including rotatable locking rings. Each cartridge having a distinct filtering characteristic includes a keying structure to ensure that the cartridge can only be connected to the manifold for placement in proper serial-flow relationship in the system. The filter system includes a spent filter cartridge indicator. The filter system is particularly suited for countertop placement and connection to a faucet.