Thermostatic mixing valves are used to maintain hot water supplied to the user at a constant and safe temperature when variations in the hot and cold water supply conditions and draw off flow rates occur. This arrangement also allows hot water to be stored at a sufficiently high temperature in the water heater to prevent bacteria growth such as legionella, whilst mixing hot and cold water together close to the outlet at a temperature of typically 38-44 deg C to prevent scalding the end user, especially vulnerable persons such as the elderly, children or those with impaired mobility. Thermostatic blending valves also allow the extension of effective stored hot water capacity by mixing high temperature water with cold to a pre-determined temperature level.