Abstract: This invention relates to a device for a household water purifier in which raw water is pressurized and is filtered by means of inverted osmosis, ultra or nanofiltration or the like. The device is provided with a central unit having a first part (10) comprising a vane pump (12) with a pump housing (16) and a second part (11) comprising a filter connected to the first part. The first part (10) is shaped of plastic or the like and the pump housing is (16) at least partly surrounded by a liner (17), which consists of a material which differs from the material of the pump housing, and the liner (17) is at least partly surrounded by the first part (10).