We're in a race to build first new reservoirs in decades before Britain's taps run dry

On the night of 14 May 1943, something new and terrifying hurtled towards the dam holding Abberton Reservoir in place. Flying at a well-calculated 232mph and altitude of 60ft, the Lancaster bombers of 617 Squadron RAF Bomber Command made their approach, but did not drop their bouncing bombs. That would happen two nights later in the Ruhr Valley, when they carried out Operation Chastise, when 53 airmen and 1,600 civilians lost their lives in Germany. 

Historians differ over whether it changed the course of the war, but had Britain not spent the time from the Industrial Revolution to the start of the 20th century building reservoirs, it’s unsure whether the Dambusters would have had anywhere to practise. Eight decades on, those reservoirs – from Colchester to Derwent – are still in use. As climate change and drought threatens the UK’s water supply, they are becoming more critical than ever. In meeting rooms and computer simulation programmes, a battle is being fought to meet the challenge. 

Estimates suggest that by 2050 there is a one in four chance households will see their water supply cut off for an extended period, thanks to severe drought. Guarding against this will require adding an extra million litres per day to the water supply, the National Infrastructure Commission found in 2020. By 2030, new water supplies will be needed roughly equivalent to the water consumed by nine million people. That means building new reservoirs. 

The country has largely forgotten how to do this. In 1989, Margaret Thatcher’s government privatised the UK’s water companies. In the 35 years since, just one potable water reservoir has been completed – Carsington Reservoir in Derbyshire, in 1992. 

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In fact, in recent years, water companies have even been selling off reservoirs. And just this year, Clydach reservoir in Wales has been decommissioned, with Welsh Water planning to turn it back into a natural lake.  

“The thing people probably don’t realise is how old the reservoirs are in the UK. I think people think of reservoirs and they think of a shiny new water supply reservoir,” explains Rachel Pether. 

Pether is an ‘all reservoir panel engineer’ – a designation given to a select group of engineers who inspect and oversee the country’s reservoirs, from back garden ponds and National Trust ornamental lakes to drinking water storage. 

“But actually, 99% of my time is spent looking at reservoirs that are over 100 years old. That in itself is a massive challenge,” she says. 

“When most of the last batch of reservoirs were designed in the 1970s, people were either still doing calculations by hand, or they had computers where you put something into the computer, went away for a day, and came back the next day to get an answer. And the computer took up a whole room.” 

Any body of water holding more than 25,000 cubic metres of water above ground level counts as a reservoir. Its construction and design is overseen by all reservoir panel engineers, who will inspect it every 10 years. In the case of older reservoirs, Pether might be lucky to get her hands on a single drawing outlining how the dam was made. 

Reservoirs are nationally important infrastructure. It might not be a surprise to learn they are a pain to build, often costing in the billions and taking over a decade. A dam is not just the kind of imposing concrete wall which has nightmares of (bouncing bomb inventor) Barnes Wallis, it is also the bit above ground level keeping the water in. Picture the nice embankment fishermen sit on. 

Building this requires what’s known as an earth-moving plant, similar to the machines used to widen motorways. Layers of material, often clay and sourced on site, will be flattened and compacted into an impermeable core, with pipes laid to get the water out. Even getting to this point is a challenge. 

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“Once you’ve decided you want to build a reservoir, that’s significant. It’s an engineering challenge, and it’s obviously very costly. But it’s also in terms of the land, and getting that through planning. That’s a big project in its own right,” says Pether. 

“Other than, say, the nuclear industry, I don’t think there’s any other type of infrastructure where the design and construction process is as tightly regulated.” 

Planning can be tricky. On the same night as the Abberton dress rehearsal, six crews from 617 Squadron practised their low approach over the Derwent Reservoir, a stand-in for Germany’s Sorpe Dam. Last year, plans to expand this 1900s reservoir were abandoned following campaigns from locals who worried it would “desecrate the heart of a national park”. 

Privatisation has also played a role in stopping new reservoirs getting built, says Wouter Buytaert, Professor in Hydrology and Water Resources at Imperial College London: “This has led to a reluctance for long-term planning and large investments, in favour of short-term gains such as dividend payouts. The situation of Thames Water is a case in point,” he says. 

The investment needed could run to £21 billion, likely to come from the pockets of bill-payers. But Buytaert argues not doing it would be more costly. “If reservoirs are not built then we’ll pay much more for our water,” says Buytaert. And so, faced with a future of drought and taps running dry, in 2019, the water companies, Environment Agency, water regulator Ofwat, and Drinking Water inspectorate joined forces to form RAPID (Regulators’ Alliance for Progressing Infrastructure Development). Their task was to remove the barriers that have stopped reservoirs and major water infrastructure being built. Progress has begun. 

Havant Thicket, the first new drinking water reservoir in three decades, is under construction near Portsmouth. When it opens, 160,000 residents of southern England will be supplied with 21 million litres of water every day. Anglian Water is building two new reservoirs, at a cost of £3.3bn. Plans are afoot for new sites in Oxfordshire and Lincolnshire. Cheddar Two, a new reservoir in Somerset, is in the works. 

Existing reservoirs are being upgraded too: Essex and Suffolk Water recently raised the dam of Abberton Reservoir, increasing the amount of water that can be held there. Innovative pro-jects are being explored, like the Mendip Quarries, which will turn a quarry south-west of Bristol into a reservoir. 

“Not all holes in the ground are suitable for holding water, but with this one the geology is really well suited. You’re already halfway there, aren’t you?” explains Paul Hickey, the managing director of RAPID. 

Much of the work involves looking beyond the interests of a single water company. Instead, a move to looking at the needs for whole regions has been “transformational”, says Hickey. For example, the South East has been designated as being in “serious water stress”. By 2030, a total of seven regions – including the West Midlands, the East of England, and London – are anticipated to be severely water stressed. 

Water companies are learning to cooperate. Havant Thicket is being built by Portsmouth Water, but will mostly benefit Southern Water. A new project in Oxfordshire could potentially serve four water companies. This means getting them to share the risk, and make sure construction is competitively tendered, explains Hickey. 

Reservoirs are one part of the solution. Getting us all to consume less water will be key, Hickey says, as will transferring and transporting water. Beyond drinking water, reservoirs can provide new habitats for nature, resources for agriculture and industry and relieve pressure on other sources. 

“I do believe there is a growing acceptance that we need to do such projects,” says Hickey. “We’ve got housing and wider economic development being stopped in Cambridge because of a lack of water resources. That’s one link to one of our new projects, which is to build a new reservoir in Cambridge to alleviate that situation. 

“What will be fantastic once that project comes is, all the water at the moment for Cambridge comes from chalk streams. These are globally rare habitats being impacted. 

“If we want to do things like prevent damage to iconic habitats like chalk streams, we need to get our water from other places.” 

The new generation of reservoirs will be very different from the last. Hand-drawn plans are out, replaced with digital models run through computer simulations and fed into automated machinery. And, pleasingly, instead of death-defying Lancaster bombers, these days visitors are more likely to spot birds, bees, and otters skimming the water. 

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