Single fault at Thames Water works could imperil London’s supply

Thames Water’s main treatment works in the British capital is so vulnerable that just one system failure could leave millions of Londoners without running water.

Mass evacuations, with the military on standby, could be triggered in the event of a failure at the crumbling Coppermills works in north-east London, according to people with knowledge of the site.

Water outages for millions of people across the twin financial centres of Canary Wharf and the City of London could be prompted by a single fault, according to documents seen by the Financial Times.

Thames Water, which is struggling under its near-£20bn debt pile and is trying to avoid renationalisation, has pledged to replace the 60-year-old pumping system at Coppermills and install advanced ultraviolet filters to improve water treatment.

But the fact that a £400mn project to upgrade the leaking plant, which serves 3mn-4mn Londoners, is now only just beginning has raised the risk of a catastrophic failure, the people said.

Coppermills lays bare the scale of the challenge for any buyer of Thames Water, which is in the hands of its senior creditors after private equity firm KKR walked away from a rescue bid earlier this year.

The 1960s plant in Walthamstow is on a list of 13 critical infrastructure water treatment and sewage processing sites belonging to Thames Water at risk of “single point of failure”, meaning that only one incident could disrupt supplies, according to people familiar with the facility and internal documents.

Several of these plants are linked through a circuit known as a ring main. The idea of the circuit is to improve water resilience but the structure means that disruption at one could cause knock-on effects at others.

Water regulator Ofwat has described the “loss of Coppermills” and resulting “supply deficit” in north-east London as “a low-probability, high-consequence event”, according to a 2019 document. The watchdog added that Thames Water had estimated the probability of failure as a one-in-50-year event, but was “not clear what was assessed, nor how this figure was arrived at”.

Sir Jon Cunliffe, a former deputy governor of the Bank of England, said in a speech announcing the findings of his independent review into the water sector in July that the facility that supplies all of Canary Wharf “is on its last legs”, adding that the fact the site is only now being overhauled is indicative of “a patch and mend approach”.

Cunliffe told the FT after his speech that when he visited Coppermills earlier this year, water was leaking into the engine hall that houses electrical pumps.

“I’m not suggesting it will fail,” Cunliffe said, “but why is this [work] just starting now when I can see the water coming through the roof and they’re telling me it’s been like that for years?”

Awareness of the perils of a single point of failure for infrastructure assets has been heightened in the wake of a power outage that grounded flights for more than 24 hours at Heathrow airport in March this year.

Coppermills relies heavily on a pumping station built in the 1960s that cannot be repaired without “interruption” to customer supply, according to an April presentation to investors. Thames Water also warned in this document that a “significant mechanical or structural failure” of the pumping station “could result in supply interruption to customers”.

Construction of the new pumping station is not scheduled for completion until the start of 2031.

Another complicating factor is that critical pipes sitting above the room housing the pumps are entombed in concrete, making it harder to fix leaks that are now seeping through the roof. In 2019, Ofwat said that a steel pipe encased in concrete in the pumping station was a “common inlet and outlet manifold and thus is a single point of failure”.

Another person who inspected the site earlier this year described his shock at seeing “a cascade of water” behind an electrical panel in the pumping station.

In most cases, when a water treatment plant fails, it is possible to mitigate the impact by rerouting water from other works, delivering water to local reservoirs by tanker, or distributing water in bottles.

But the potential scale of any outage at Coppermills is so large that people may need to be evacuated from their homes, with the military on standby, said two former staff members who had worked closely on the plans for the site.

Both added that Thames Water had known of the issues at Coppermills for at least a decade, while documents submitted to Ofwat in 2019 point out the “deteriorating water quality” at the treatment works and the need for urgent investment.

Thames Water said in a statement: “Thames Water has the oldest and most complex assets in the country and that is why we have embarked on the largest ever investment programme, delivering the biggest upgrade to our network in 150 years. We have ambitious plans to deliver improvements over the next five years by investing more than £20bn to address asset health.”

It added that its £400mn project “is part of our planned investment to secure the ongoing resilience of our assets in light of London’s growing population and climate change. Taken together, these investments will help secure an ongoing supply of safe, clean, wholesome drinking water to our customers.”

Ofwat declined to comment.

The new UV filters at Coppermills are intended to prevent water becoming contaminated with cryptosporidium — an infectious disease that causes vomiting and diarrhoea.

One former Thames Water staff member told the FT that the situation at Coppermills was “scary” and there was “no way that there are enough bottled water supplies” to deal with an outage.

The person who recently inspected the site also said that the size of the population it serves would make it practically impossible for the army to hand out bottled water if there were a catastrophic failure.

He added: “Can you imagine if 4mn people can’t flush the loo or use the shower?”

Thames Water itself has identified north-east London, which for its purposes includes the City and Canary Wharf, as its “highest risk zone, with the risk of large-scale interruptions to water supply”, according to a separate 2019 document.

Several of London’s other water treatment plants also require urgent work to avoid risking a shortage of acceptable supplies to Londoners. This includes the need for investment to reduce the risk of cryptosporidium at the Hampton and Ashford Common water treatment works in west London.

The Hampton works also need a new pumping station and power supply upgrades, according to a map of 13 at-risk sites drawn up as part of investor due diligence earlier this year.

KKR walked away from its bid for Thames Water in June, citing the risk of government intervention. That has left the UK’s largest water utility in the hands of its senior creditors, which include the hedge fund Elliott Management. They are trying to convince regulator Ofwat and the government to endorse their proposed takeover of the utility.

They have asked regulator Ofwat for more leniency on sewage pollution targets and have requested delays to mains repairs.

The creditors are aiming to exit the business and list the company on the London Stock Exchange as early as 2030.

For its part, Thames Water has said that its transformation “will take time; it will take at least a decade to achieve the scale of change required.”