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Forever chemicals surge during Thames Water drought pilot

newsAug 27, 2026261,125

Thames Water piloted a plan to abstract up to 75 million litres a day from the River Thames at Teddington during droughts and replace it with treated sewage from the Mogden treatment plant; pilot tests recorded the forever chemical perfluorooctane sulfonate PFos at 6.3 and 8.7 nanograms per litre, breaching the UK surface-water legal limit of 0.65 ng/L by as much as 13 times. Technical notes seen by the Guardian show PFos rose rapidly, with a "rapid breakthrough" above the legal threshold in less than one month of operation. Thames Water says the recycling project, for which it is seeking a development consent order, would not harm the river, but the company’s documents concede keeping PFos within legal limits would be "operationally challenging" and would require frequent regeneration, reactivation and replacement of carbon filters and "significant additional operational expense." The pilots also found very high levels of iron that the company’s own note warned would have a "significant detrimental impact" on the river. The scheme is budgeted at at least £350 million and the company contrasted the 75 million litres a day abstraction with its reported 571 million litres lost to leaks each day. Campaign group Solar, which opposes the project, said the pilot results show Thames Water cannot make the scheme "work properly." Thames Water continues to pursue planning permission through the development consent process while regulators and local stakeholders assess the environmental risks revealed by the pilots.

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