Experiments to determine the net energy contribution of the domestic water system to internal heat gains of a house are reported. Four water use profiles and two cold water supply temperatures were considered. For a typical water consumption schedule, apart from hot water tank standby losses, gains from water use are very small. In most cases they can be neglected, particularly where the average cold water supply temperature is low (less than about 10°C), as is typical of most locations in Canada and the northern United States.