Abstract: The water purification apparatus of this invention is used in combination with a domestic hot water heating tank and comprises a water container mounted on top of the tank. Hot tank water is supplied to the container through a passage controlled by a float-actuated needle valve. Water in the container receives additional heat from a heat-radiating pipe which extends from the tank through the container and back to the tank to maintain a continuous circulation. Water vapor formed in the container is carried away through a duct and condenses. A receptacle is provided for receiving condensate from the discharge outlet of the duct.