Abstract: A system is shown for providing domestic hot water for potable use. The energy source is a steam powered heat exchanger. Water is heated in a heat engine package including the heat exchanger, a temperature operated pump and a condensate control valve. The heat package works in conjunction with a water storage package including a water storage tank and an electronic controller which controls the operation of the pump and condensate control valve. The electronic controller is operated so that the control of steam supplied to the system and flow of water through the heat exchanger ensures that steam is only present in the heat exchanger when there is a predetermined high flow rate of water.