A process for desalinating water is disclosed. The process comprises the steps of passing a feed stream of saline solution 2′ in a first desalination step through a reverse osmosis membrane desalination plant 3′ comprising at least one reverse osmosis desalination unit 4′ to form a first product water stream 5′ having a reduced salt concentration relative to that of the feed stream of saline solution 2′ and a first byproduct stream 6′ having an increased salt concentration relative to that of the feed stream of saline solution 2′ characterized in that the first byproduct stream 6′ is passed in a second desalination step through a falling film crystallization unit 7 to form a second product water stream 8 having a reduced salt concentration relative to that of the first byproduct stream 6′ and a second byproduct stream 9 having an increased salt concentration relative to that of the first byproduct stream 6′. The invention further relates to an apparatus 1 for carrying out said process. The present invention further relates also to the use of the process or apparatus 1 for the reduction of the volume of the first byproduct stream 6′ of a reverse osmosis membrane desalination plant 3′, preferably an in-land desalination plant 3′, or in a device or plant or process for producing desalinated water, for salt production, for co-production of power and desalinated water, or for air conditioning.