Provided is a method of signalling a command to a water heating appliance remote from a controllable water outlet fed from the appliance via a water supply installation, the method comprising: monitoring the water supply that feeds the controllable water outlet; detecting a sequence of changes in a property or state of the water supply consequent on operation of the controllable water outlet; correlating the sequence of changes with a stored pattern; detecting a match above a stored threshold; interpreting the match as a command. It is thus possible to manipulate a tap, or other controllable water outlet, to signal to a processor so that the temperature or flow rate of water supplied by the outlet can be increased. Thus a water supply system may have default flow and temperature levels designed for economy and low water usage, but a user can on demand override one or both of these limitations without the necessity of needing to go to the appliance to reset it. The water heating appliance is preferably an instantaneous water heating appliance. Also provided is a water supply installation including a water heating appliance, a controllable water outlet remote from the appliance, a water supply line arranged to feed the controllable water outlet with heated water from the appliance, and at least one sensor to sense a property or state of the water supply line, and a processor coupled to the at least one sensor; the processor being configured to detect a sequence of changes in a property or state of the water supply consequent on operation of the controllable water outlet; correlate the sequence of changes with a stored pattern; detect a match above a stored threshold; interpret the match as a command; and take an action in accordance with the command.