Methods and systems and apparatus to support reduced energy and water usage

A method of signalling energy usage to a user of a hot water outlet of a hot water supply system, the hot water supply system including:

• a thermal energy store that is supplied with energy from a source of renewable energy;
• a renewable energy source;
• an auxiliary water heater coupled to a networked energy supply;
• a flow transducer operable, when a water flow passes through the hot water outlet, to provide flow rate data for the water flow;
• and
• a processor coupled to the flow transducer;
• the hot water supply system being operable, under the control of the processor, to heat water that is to be supplied to the hot water outlet to a target system supply temperature using a selection of one or more of the auxiliary water heater, the renewable energy source, and energy from the thermal energy store;
• the method comprising:
• determining that water is flowing through the hot water outlet, and determining a corresponding flow rate;
• determining the selection required to maintain the target system supply temperature at the flow rate demanded by the user at the outlet;
• classifying the selection into one of at least two categories, and/or determining the energy usage against a scale of usage;
• signalling to a remote light source visible in the vicinity of the outlet a colour based on the classification or on the determined energy usage;
• and
• heating water using the selection.