PURPOSE: To easily produce drinking water, etc., by transmitting solar heat to water, etc., in a heat insulating water vessel to evaporate the water, liquefying the vapor in a cooling vessel, collecting the condensate in a trough, pouring the condensate into a storage tub and automatically replenishing water in amt. equivalent to that of water evaporated.

CONSTITUTION: A plate A having excellent heat conductivity is exposed above the water surface L and the heat is transmitted to the water, etc., in an underwater heat insulating water vessel D which is hardly heat-exchanged with the outer periphery by using a conduit B connected to the plate and with less heat loss to evaporate the water. The vapor is liquefied in an underwater cooling vessel F consisting of a material easily heat-exchangeable with the outer periphery and communicated with the water vessel D. The condensate is collected in a trough O and poured into storage tubs P and Q with a pipe W. In this case, the feed of water and the discharge of condensate are automatically carried out by the opening and closing of a water feed valve J and a water discharge valve K of the vessel F which are connected to a float I moving in follow-up to the water level moving vertically in the water vessel D. Water, an org. solvent, etc., can be distilled in this way.