Abstract: A filter apparatus for a home reverse osmosis water system is provided. The apparatus has a head, which has a forward flow inlet port for connection to a reverse osmosis water unit, and which has a reverse flow outlet port for connection to a water service faucet. The apparatus also has a cartridge, which has a twist-on securing means for connection to the head, a filter assembly for filtering forward fluid flow and for filtering reverse fluid flow, and a combination inlet and outlet port for connection to a pressurized water tank. The filter assembly has a primary filter unit, which is disposed in a cartridge primary chamber, and a secondary filter unit, which is disposed in a cartridge secondary chamber, and a valve means, e.g.