Washrooms are a significant source of water waste; early design decisions can determine how buildings perform for decades, so specifications must tackle both usage and leakage to reduce consumption. Richard Braid at Cistermiser explains.

Energy performance has long dominated design discussions, but water efficiency 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 five billion litres.

Policy is beginning to reflect this change. The Government’s recent White Paper sets out a strategy aimed at improving water efficiency 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 specified; water efficiency cannot be resolved through management alone if the underlying specification works against it.

Continuous flow: 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 specified 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 flow (where the meter shows a reading of 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 flush at fixed 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 flush cycle when a facility is used, removing the water waste associated with timed systems.

Retaining automatic flushing in new or refurbished buildings effectively builds in inefficiency from day one. In contrast, occupancy-based controls match water use to demand, improving performance and reducing cost. WCs can be another problem; leaks often only appear as small trickles down the back of a loo which can be difficult to spot. But a single leaking toilet can waste up to 400 litres daily.

Traditional drop-valve systems rely on seals that lie below the waterline. This means they are prone to deterioration as scale and debris builds up. Choosing a flushing valve that doesn’t have a flush seal below the waterline means the seal won’t degrade and it won’t leak.

Leaking cisterns are another frequent issue, because the standing water makes them vulnerable to scale and impurities, which can quickly accumulate and compromise the watertight seals. Direct flushing removes the need for a cistern entirely. Instead, it uses mains pressure to give an effective, controlled flush. Without a stored volume of water, the risk of leakage is removed along with many maintenance requirements associated with cisterns.

Part G of the Building Regulations sets out requirements for water efficiency, hygiene and safety. Compliance is often achieved at handover, but performance needs to be maintained over time, and that depends on the durability and suitability of the installed systems. The growing use of smart metering will make this more visible. As more buildings are closely monitored, actual usage will become harder to ignore. Continuous flow, excessive flushing and undetected leaks will all appear in the data.

This has implications beyond utility costs. ESG reporting is placing greater emphasis on operational performance, with water use forming part of broader environmental metrics. Buildings that fail to perform as intended may fail to meet client expectations or regulations over time.

As the industry responds to tightening targets and greater transparency, water efficiency is likely to receive the same level of attention as energy performance. Washrooms may be a relatively small proportion of total construction cost, but they have a disproportionate impact on water consumption. Early specification decisions carry long-term consequences. Selection must involve assessing how systems will operate over time, how they respond to real patterns of use, and how they contribute to overall building efficiency.

Richard Braid is managing director at Cistermiser