Abstract: A low pressure distillation apparatus in which evaporation takes place at sub-atmospheric pressures. An evaporation chamber has a feed liquid inlet port, a concentrated liquid outlet port, and a vapor outlet port. The vapor outlet port is in communication with a vapor treating device immersed in distillate in a distillate chamber. The preferred vapor treating device is a rotating impeller pump which reduces the pressure in the evaporation chamber to a working pressure, draws off vapor boiled from the liquid in the evaporation chamber, entrains the vapor in a stream of distillate, and condenses the vapor in the stream of distillate to transfer the latent heat of condensation of the vapor directly to the distillate.