Third of Thames Water sewage sensors are faulty, analysis reveals

A third of Thames Water sewage monitors do not properly function, new analysis of official data has revealed.

The latest revelation over Thames Water was part of data which showed a record number of sewage spills across the UK last year following wet weather.

The UK’s largest water company – which supplies around a quarter of the UK population in London and the southeast – is responsible for almost 17,000 raw sewage spills in 2023, a 112 per cent increase on the previous year and accounts for the biggest relative increase since 2022 of any UK water company.

But the total number is likely to be underestimated as across the industry about 2,200 (15 per cent) of the 14,500 sewage monitors on storm overflows do not function properly. At Thames Water, around 33 per cent of the company’s monitors do not correctly function, according to analysis of Environment Agency data by the Liberal Democrats.

The monitors identify and count flows of sewage discharged into rivers and the sea. They are required by regulators to work more than 90 per cent of the time.

The second and third worst performing companies for sensor failure were Southern Water and Yorkshire Water, both of which have a failure rate of around 18.5 per cent. Wessex Water was the best performing, but still had 4.4 per cent of its monitors not correctly working.

A specific Southern Water monitor, meanwhile, only worked for 30 per cent of last year after not functioning throughout 2022. Another Northumbrian water in County Durham has been out of action for two years now, according to the data.

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It comes after the crisis at Thames Water depended on Thursday after shareholders refused to provide a £500 million cash injection into the beleaguered utility company.

Thames Water said it had until late next year to secure additional funding and stabilise its finances. Failure to do so would see the government intervene and potentially place the company into special administration. It also more than likely faces nationalisation.

Following analysis of the new data, environment spokesperson for the Liberal Democrats Tim Farron MP accused water companies of potentially being “complicit in an environmental cover-up”.

“Why on earth would a firm install these monitors if they don’t even work?,” he said, adding: “The scale of the sewage scandal could be even larger than originally feared.”

Mr Farron, the former Liberal Democrat leader between 2015 and 2017, accused ministers in the Conservative government of not being “interested in understanding the true extent of the damage our rivers and beaches are being put through”.

“They have let water companies off the hook at every turn and are now letting them get away with not even monitoring the amount of filthy sewage that is being dumped.

He also called for “a national environmental emergency to be declared” to address damage inflicted on waterways by sewage flows.

A spokesperson for Water UK – which represents utility companies like Thames Water – told i: “Water companies are committed to robust monitoring of storm overflows across England with all now monitored – the most comprehensive and extensive monitoring system in the world.

“Due in part to their operating outdoors and in all weather conditions, some monitors will occasionally be temporarily out of action while maintenance is underway. This has improved, and the regulator has taken tough new powers to ensure the highest standards.

“We are seeking regulatory approval to invest over £10 billion over the next five years – three times the current rate – to increase the capacity of our sewers and remove more than 150,000 annual sewage spills by the end of the decade.”

Thames Water was approached for comment separately by i.