Abstract: A tank for receiving water to be desalinated supports a vacuum pump at the upper end thereof. The inlet of the pump communicates with the tank for reducing the interior of the tank to a subatmospheric pressure and the outlet of the pump communicates with heat transfer coils submerged just below a water level in the tank. The vacuum pump has an outer casing defining a heating area which traps the heat generated by operation of the pump. An inlet for water to be desalinated leads through the heated area around the pump and is discharged above the water level at the heat transfer coils for vaporization of the incoming water. The heat transfer coils communicate with condensing coils leading downwardly in the tank. The heat transfer coils are supported on a float and have an inlet and outlet arrangement providing for even distribution of vapor.