INTERIORS 59 Designing out water waste
Washrooms are a signifi cant source of water waste; early design decisions can determine how buildings perform for decades, so specifi cations must tackle both usage and leakage to reduce consumption. Richard Braid at Cistermiser explains.
E
nergy performance has long dominated design discussions, but water effi ciency is moving up the
agenda. It’s not before time; the UK might have plenty of rainfall but it still faces a growing water shortage.
The drought of 2022 saw temperatures reach record highs, river levels record lows and reservoirs fall to around 65% of typical summer levels. It wasn’t an isolated event. The spring of 2025 was one of the driest on record, and computer modelling suggests these conditions will only become more frequent. An ageing infrastructure, population growth, climate change and the demands of emerging technologies like data centres are placing huge pressure on water supply. By 2055, the daily shortfall could reach around fi ve billion litres. Policy is beginning to refl ect this change. The Government’s recent White Paper sets out a strategy aimed at improving water effi ciency to reduce customer bills, safeguard future supplies and protect the environment. Water entering public supply is to be reduced by 20% by 2038 and per capita consumption to 122 litres per day; 110 litres by 2050. Non-domestic buildings are not overlooked; targets have been set to reduce business water use by 9% by 2038 and 15% by 2050. This requires meaningful changes in how buildings are designed and specifi ed; water effi ciency cannot be resolved through management alone if the underlying specifi cation works against it.
Continuous fl ow: a built-in cost Washrooms are a clear example of where design intentions and operational reality can diverge. Despite being high-use spaces, they are frequently specifi ed using familiar, traditional approaches that allow avoidable waste to continue.
Smart meter data provides useful insight; showing between 25% and 30% of water use in commercial buildings is continuous fl ow (where the meter shows a reading of
ADF JUNE 2026
one litre per hour or more, every hour, for 14 consecutive days or longer). Although this can be genuine usage, in many cases it points to leaks or unnecessary waste. Urinals are a major culprit. Traditional systems often fl ush at fi xed intervals, sometimes as frequently as three times per hour, regardless of occupancy. Over the course of a year, this can amount to hundreds of thousands of litres of treated water being discharged without purpose. Sensor-based systems work are a solid solution to this problem; Thames Water suggests that sensor controls can reduce water consumption by up to 80%. They only activate a fl ush cycle when a facility is used, removing the water waste associated with timed systems. Retaining automatic fl ushing in new or refurbished buildings effectively builds in ineffi ciency from day one. In contrast, occupancy-based controls match water use to demand, improving performance and
Smart meter data shows that between 25% and 30% of water use in commercial buildings is continuous fl ow
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