Thames Water sewage data show hundreds of illegal spills

Thames Water, the UK’s biggest water company, illegally discharged untreated sewage into rivers on two out of every three days over the past three years, according to analysis of the company’s spill data.

The Environment Agency allows water companies to discharge some untreated sewage into rivers via storm overflows when rainfall runoff from roads and roofs overloads a sewage works. This is partly to avoid sewage backing up into homes.

However, they are prohibited from making “dry spills” of untreated sewage when there is no rainfall or “early” spills of sewage discharged when a works fails to maintain a minimum rate of treatment.

A detailed analysis of sewage treatment and spill data over the past three years showed that the environmental regulator has recorded just 33 “dry” and “early” breaches by Thames Water over the past 11 years, even though the analysis claims there were dry and early spills on 735 days at 13 of the company’s sewage treatment facilities in West Oxfordshire and the Cotswolds between 2018 and 2020.

The data, collected by the Windrush Against Sewage Pollution Campaign Group in Oxfordshire, suggests that 95 per cent of dry and early sewage spills go unrecorded. Since 2008 the government has relied on water companies to report any unauthorised discharges. By the Environment Agency’s own admission many go unrecorded.

Professor Peter Hammond, a former professor of computational biology at University College London, who carried out the research for Wasp and has appeared at several parliamentary hearings on water, said the discrepancy demonstrated the inadequacy of the EA’s detection of illegal spills.

“Furthermore, it suggests the annual Environment Performance Assessment of sewerage operators, a key element of the financial regulation of the water industry by Ofwat and the EA, is based on incomplete data and is like a house built on sand,” he added.

Thames Water said it regarded all discharges of untreated sewage as “unacceptable” and was trying to “accelerate work to stop them being necessary”. “Our planned investment in our sewer network and the upgrading of sewage treatment works across our region . . . will help improve the situation,” it added.

Most illegal discharges go unprosecuted but Thames Water was fined £20m in 2016 for tipping 1.4bn litres of raw sewage into the Thames and its tributaries in a case that the judge ruled was “borderline deliberate”. It also received fines for pollution of £2m in 2018 and £2.3m in 2021.

Court actions brought by the EA for water offences have been declining, with nearly all convictions brought about as a result of members of the public pressing for action.

The decline in prosecutions comes despite EA figures showing that just 14 per cent of England’s rivers met the minimum “good or better” ecological status in 2019.

The EA said it was reviewing 12,000 storm overflows to identify those operating in dry weather or non-compliant with permit requirements. “This will filter out storm overflows which are of concern so we can request further information from the water companies to assist with our investigations,” it said.

Southern Water was fined a record £90m for pollution this year. Ofwat had already found that it had manipulated water samples and “deliberately misreported data” for seven years until 2017 to avoid financial penalties. The company had also used tankers to shift wastewater from problematic sites to avoid submitting poor readings to the EA.


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