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An On the wire story
Waterwise and the Water Research Centre estimate that households may lose hundreds or thousands of litres each year while waiting for hot water to reach taps, showers and other outlets.
Their model puts annual losses at 847 to 2,124 litres under standard operating conditions, rising to between 1,321 and 2,599 litres in scenarios where energy-saving modes are used. These are estimates based on modelled situations, not measurements from a representative sample of occupied homes, and the actual amount will vary between properties.
The research examined new-build layouts and found that the position of a boiler or other hot-water source, the distance to outlets and the arrangement of pipework can all affect how long people wait. Frequent use may matter as much as the volume released at any one time: although showers and baths can run more water before it warms, taps in kitchens, bathrooms and WCs may account for greater losses because they are used more often.
Engineering research has also linked delivery times and heat loss to pipe configuration, insulation and household use. Measurements in several homes for a separate study found that 2.9 to 5 litres could be drawn before water reached the desired temperature, with waits of 17 to 47 seconds; the small sample is not a national estimate.
The concern is not new. A 2013 paper by researchers N. R. Nawaz and B. C. K. Waya estimated that water discharged while waiting for hot water represented about 10% of average daily household water use per person in the UK. Its methods and assumptions differ from the Waterwise and WRc modelling, so the figures should not be treated as directly comparable.
The earlier work nevertheless underlines that water lost during the wait has been recognised as a potential demand-management issue for more than a decade.
Waterwise says that better positioning of hot-water sources and more compact pipe networks could reduce losses in new homes. In existing properties, insulation, efficient fittings and changes in household routines may help; collecting the initial cold water for another use is one option.
The research also highlights a potential trade-off: switching off a boiler’s preheat function to save energy may mean more water is run before it becomes hot. Waterwise and WRc say further monitoring is needed before the findings can support changes to building regulations, alongside consistent measurement standards and design guidance. The study reviewed CombiSave as an example of a product, but did not test or endorse it.
References
Main reference: Waterwise [1]
• This On the wire article was created using Noahwire AI and reviewed by CIBSE Journal’s editorial team
