The present disclosure relates to a water purification apparatus that comprises a reverse osmosis device, RO-device, producing a purified water flow and to a corresponding method. The proposed method comprises detecting at least one fluid property of purified water in the purified water path and regulating a flow rate of water in the recirculation path to fulfill one or more predetermined criteria of the purified water in the purified water path, based on the at least one detected fluid property. The present disclosure also relates to a computer program and a computer program product implementing the method.