Building Systems Thinking: Our water and wastewater systems need replumbing

Following a parched summer last year, many feared that 2026 would bring severe drought. A wetter than average winter instead brought flooding, while replenishing aquifers, river flows and reservoirs. Drought appears to have been averted – but water scarcity is nonetheless an increasing concern across the UK and will become worse in future. The country faces a supply shortfall by 2055 of 5 million cubic metres per day. Paradoxically, flooding is a growing problem.

The proposed solutions include vast new reservoirs and transfer pipelines for water supply; massive underground tanks and treatment works for stormwater management; and improved flood protection. All requiring large quantities of concrete and steel, vast earthworks, bigger pipes, more pumping, more energy, more chemicals. Together, the water industry’s planned programme of works forms one of the most carbon‑intensive infrastructure investment programmes this country has ever embarked upon.

And here’s the problem. As we know, carbon emissions drive climate change, so the programme will contribute to worsening the challenges it seeks to address. Meanwhile water scarcity, flooding and storm overflows are interlinked. The programme tackles the symptoms of our combined crisis in silos and far away from where it actually begins, which is our homes, streets and buildings.

Building a problem into existence

The crisis is rooted in the way we have designed them for decades, and continue to do so.

The uncomfortable truth is this: the UK overall does not lack water. It lacks the ability – or political will – to manage rain where it lands.

On average, enough rain lands on every roof each year to meet all of that household’s non‑potable water needs, such as flushing toilets, washing cars and watering gardens. Yet we persist in supplying high‑quality drinking water to homes, simply to urinate and defecate into it, and flush it away again.

Around a quarter to a third of domestic water supplied is used this way.

The energy involved simply in moving water around is huge – it’s the equivalent of every single person in the UK lifting a 1kg weight one and half times the height of Mount Everest, every single day

Drinking water is taken from the natural environment, often many miles from where it will be used. On the way it is treated with chemicals and energy‑hungry processes. As a national average, moving water from point of abstraction, through treatment, to point of use involves lifting it through a combined height of around 100 metres. The average Brit uses 137 litres of the stuff each day. The energy involved simply in moving water around is huge – it’s the equivalent of every single person in the UK lifting a 1kg weight one and half times the height of Mount Everest, every single day.

And our current strategy is to do more of the same. The industry is spending tens of billions of pounds on reservoirs to hold a bit more rain, so we can treat more of it, pump more of it to our homes and keep on filling our toilets with it.

At the same time, homes, driveways and roads send vast volumes of rainwater straight into our drains. There, it mixes with sewage, increasing the volume of wastewater that has to be pumped and treated. And when the volume exceeds the capacity of the treatment system, it gets discharged through storm overflows into rivers or the sea. Our wastewater treatment plants can cope with the sewage we produce. It is the rainwater that causes the system to overflow.

To be absolutely clear, rainwater does not require treatment. It should not be allowed to run into the systems that carry sewage. Doing so creates problems for everyone – water companies, the environment and society together.

Land is being covered with impermeable surfaces. Developers are legally entitled to discharge rainwater to sewers. We continue to quite literally build the problem into existence

New housebuilding, urban development and changes to the existing built environment are exacerbating a bad situation. Land is being covered with impermeable surfaces. Developers are legally entitled to discharge rainwater to sewers. We continue to quite literally build the problem into existence. And the industry is spending yet more tens of billions of pounds on storage and treatment infrastructure.

Doing things differently

Contrast water with how we already think about energy. We no longer assume that all power must be generated centrally and transmitted over long distances. Instead, we actively encourage decentralised generation and energy efficiency: solar panels on roofs, batteries in homes, heat pumps, Building Regs Part L.

Whereas water policy remains stubbornly stuck in the 20th century.

In parts of Belgium, new homes must capture rainwater for use, contributing to the lowest per‑capita water consumption in Europe

Other countries have progressed. In parts of Belgium, new homes must capture rainwater for use, contributing to the lowest per‑capita water consumption in Europe. Australia, Germany and Singapore have embedded rainwater harvesting into mainstream development. England, by contrast, continues to ignore the value of rain landing on roofs and then tries to deal with it once it has become a problem rather than preventing the problem from occurring. We have Building Regs Part H, which states that foul and surface water drainage systems should be kept separate “where there is no practical alternative”. But its real‑world impact is weakened by exemptions, legacy infrastructure and inconsistent enforcement.

And it doesn’t recognise rainwater as an asset. Building Regs Part G sets out functional and efficiency requirements for water supply. Oh how refreshing it would be if Parts G and H were joined at the hip.

The alternative is not radical; it is remarkably simple and embeds the principle of source control:

• Capture rain locally and use it.
• Return excess rain to the environment as close as possible to where it lands, without ever mixing it with sewage.

Yes, it requires infrastructure: storage tanks under gardens and streets. And yes, it involves a small amount of pumping: to lift stored rainwater to fill lavatory cisterns. But the scale, energy and carbon intensity is a small fraction of that of centralised systems.

Done at scale, this approach simultaneously tackles water scarcity, water excesses and operational carbon emissions. Toilets flushed with rainwater reduce demand for new reservoirs and enable more new development. Soakaways, green roofs and property‑level SuDS (sustainable drainage solutions) slow runoff, reducing flood risk and storm overflow operation. Less pumping and treatment consume less energy and chemicals, cutting operational carbon. Less concrete and excavation mean lower embodied carbon.

Crucially, decentralised rainwater management delivers these benefits exactly where people experience them: in homes that use less drinking water, in streets that flood less, rivers that are cleaner, bills that are lower, and a whole water system that is more resilient.

Can we fix it?

None of this relies on a breakthrough in technology. Rather, it requires a shift in mindset – from designing homes that treat rain as an inconvenience to be disposed of, to recognising that rain is a resource and an asset.

And it requires regulation that focuses on environmental, social and economic outcomes.

England is about to spend unprecedented sums on water and sewerage infrastructure. We can either lock ourselves into another century of carbon‑heavy, centralised systems – or we can change our relationship with the rain that falls right on top of us all.

If we want cleaner rivers, secure water supplies, lower emissions and homes fit for a changing climate, the answer is not the construction of more centralised infrastructure. It is learning to manage rain better where it lands.

Matt Wheeldon is director of infrastructure development at Wessex Water