A method for purifying water, the method comprising: - providing a feed solution stream comprising water, having a first osmotic pressure and a temperature T 1 on a feed side of a semipermeable membrane; - providing a draw solution stream comprising a draw solute, having a second osmotic pressure and a temperature T 2 on a draw side of the semipermeable membrane, the second osmotic pressure being higher than the first osmotic pressure; - passing water through the semipermeable membrane to the draw side so as to mix the water with the draw solution stream to produce a diluted draw solution stream having a temperature T 3; characterized in that - the temperature T 2 of the draw solution stream is higher than the temperature T 1 of the feed solution stream, such that the temperature T 3 of the diluted draw solution stream is lower than temperature T 2; - at least one solar panel is provided, said solar panel comprising a heat exchange tubing system being in communication with the draw side and said solar panel having a temperature T 4 being higher than the temperature T 3; - the diluted draw solution stream is passed into the heat exchange tubing system such that the solar panel is cooled down to a temperature T 5 and the diluted draw solution stream is heated, thereby forming a heated draw solution stream having a temperature T 6; - the heated draw solution stream is passed into a separation unit such that said stream is separated into a stream of purified water and a stream of recovered draw solution; - the stream of recovered draw solution is passed to the draw side of the semipermeable membrane to be recycled, wherein solar panel is a photovoltaic panel. - providing a feed solution stream comprising water, having a first osmotic pressure and a temperature T 1 on a feed side of a semipermeable membrane; - providing a draw solution stream comprising a draw solute, having a second osmotic pressure and a temperature T 2 on a draw side of the semipermeable membrane, the second osmotic pressure being higher than the first osmotic pressure; - passing water through the semipermeable membrane to the draw side so as to mix the water with the draw solution stream to produce a diluted draw solution stream having a temperature T 3; characterized in that - the temperature T 2 of the draw solution stream is higher than the temperature T 1 of the feed solution stream, such that the temperature T 3 of the diluted draw solution stream is lower than temperature T 2; - at least one solar panel is provided, said solar panel comprising a heat exchange tubing system being in communication with the draw side and said solar panel having a temperature T 4 being higher than the temperature T 3; - the diluted draw solution stream is passed into the heat exchange tubing system such that the solar panel is cooled down to a temperature T 5 and the diluted draw solution stream is heated, thereby forming a heated draw solution stream having a temperature T 6; - the heated draw solution stream is passed into a separation unit such that said stream is separated into a stream of purified water and a stream of recovered draw solution; - the stream of recovered draw solution is passed to the draw side of the semipermeable membrane to be recycled, wherein solar panel is a photovoltaic panel.