Combination of a single reverse osmosis-unit (RO-unit) with a hemodialysis-device (HD-device), is claimed. The RO-unit comprises a filter having a membrane, which separates a primary chamber from a secondary chamber, where a raw water supply pipe opens in the primary chamber and the secondary chamber is connected to a water inlet valve of the HD-device via a connecting pipe comprising a conductivity measuring device. The concentrate output of the primary chamber leads to an outflow via a concentrate line having a flow resistance. Combination of a single reverse osmosis-unit (RO-unit) with a hemodialysis-device (HD-device), is claimed. The RO-unit comprises a filter having a membrane, which separates a primary chamber from a secondary chamber, where a raw water supply pipe opens in the primary chamber and the secondary chamber is connected to a water inlet valve of the HD-device via a connecting pipe comprising a conductivity measuring device. The concentrate output of the primary chamber leads to an outflow via a concentrate line having a flow resistance. At least one cleaning chamber for the raw water and/or for a permeate is arranged and the permeate flows into an outflow (33) when required by the HD-device (21) either through the water inlet valve (23) in the HD unit or via a flushing valve (22) of the HD-device.
