PURPOSE: To produce fresh water from sea water by using only the solar heat in an arid zone by adopting a method comprising a process of forming an evaporating chamber, a process of forming a water tank from which sea water is poured into the evaporating chamber, a process of collecting produced water, a process of taking in the sea water and a process of purifying waste water.

CONSTITUTION: In a water tank provided within a tightly closed evaporating chamber, water is evaporated from sea water due to the solar heat, and attaches to the inside wall of the evaporating chamber. Then, the water drops trickle down the inside wall and gather in a trough at the bottom. Thus, pure water containing microorganisms and organic substances is produced at a low unit cost. In order to practice this method, for example, in a desert, crossbeams are laid on foundations 1 and a water tank 2 made of steel is set up thereon, coated with a black paint for ships. An evaporating chamber is fabricated of aluminum materials, centering around the water tank 2, It is essential to glaze a roof 9, from the parts of eaves to side faces 10 and a gable and the lower parts thereof. An intake tube 12 is laid to the water tank 2, to take in the sea water from a sea 19 by means of a pump 13. In the water tank 2 inside the evaporating chamber, a computer 14 controls the concentration of the sea water, replacing it with a new one.