Abstract: Device for producing pure water, where the water to be purified is caused to be membrane distilled using one or more units (1), wherein each of the units comprises a space which on its one side comprises a first disc-shaped wall (4,4?) and on its other side a membrane (3,3?) through which gaseous water can pass but not liquid water, and a second disc-shaped wall (5,10), which walls are disposed on different sides of and at a distance from the membrane, wherein water is led in between the first wall (4,4?) and the membrane (3,3?), and wherein the second wall (5,10) is caused to be colder than the water.