Abstract: A domestic water filtration system includes a first water treatment unit (7) with a replaceable ion exchange resin water softener cartridge (15) accommodated in a canister (19) and a second water treatment unit (8) with a replaceable filter cartridge (16) including an activated carbon block (16a) wrapped with a depth filter (22a) and a membrane filter (22b). A flow control device comprising a three way valve (2) has an inlet (12) for connection to the mains water supply and two outlets (13, 14) respectively connected to the inlets of the water treatment units (7, 8) so that rotation of the valve spindle (10) in one direction from an off position allows water to flow to the inlet (3) of the first treatment unit (7) and in the other direction from the off position allows water to flow to the inlet (5) of the second treatment unit (8).