Toxic “Forever Chemicals” Surge to 13 Times Legal Limit in Thames Water Recycling Trials
A controversial £500m water recycling scheme proposed by Thames Water has come under fire after internal pilot data revealed it struggled to contain high levels of toxic “forever chemicals.” The project, intended to bolster London’s water supply during future droughts, saw concentrations of the suspected carcinogen PFOS (perfluorooctane sulfonate) spike to 13 times the legal limit during testing.
The findings, contained in technical notes seen by the media, stand in stark contrast to repeated assurances from the utility provider that its recycling plant in south-west London would pose no harm to the riverine environment.
A Breach of Standards
The recycling system is designed to abstract up to 75 million litres of water a day from the River Thames at Teddington during low-flow periods, replacing that volume with treated sewage from the Mogden treatment plant. However, because standard wastewater facilities are not equipped to filter out PFAS—a class of synthetic compounds known as forever chemicals because they do not break down in the environment—the recycling process proved difficult to regulate.
According to the documents, PFOS levels reached 6.3 nanograms per litre in the first pilot and 8.7 nanograms per litre in the second. The current UK legal threshold for surface waters is just 0.65 nanograms per litre. The technical notes describe a “rapid breakthrough” of the toxins, occurring in less than a month of operation.
Thames Water internal files admit that maintaining compliance would be “operationally challenging,” noting that it would require constant replacement of carbon filters at a significant additional cost to a company already struggling under £20 billion in debt. Furthermore, the pilots indicated that the treated water contained high levels of iron, which experts warn would have a “significant detrimental impact” on the river’s ecosystem.
Mounting Costs and Opposition
The project, originally budgeted at £350 million, is now expected to exceed £500 million. Despite mounting financial pressures and local opposition—including from local MPs and environmental campaigners—Thames Water is pushing forward with a development consent order.
Ian McNuff, a representative of the campaign group Solar, criticized the company’s reliance on the pilot results. “In essence, they can’t make it work properly,” he said. “The idea that they can switch this on and off as a completely reliable asset during drought is unrealistic against current standards.”
Industry Response
Thames Water maintains that the pilot study was merely an experimental phase intended to refine the final design. A spokesperson stated: “The data from the pilot plant study is not indicative of what would be released back into the river when the project is operational,” adding that the scheme would not proceed without securing a rigorous environmental permit.
The company also argued that the burden of removing PFAS should fall on chemical manufacturers rather than being passed on to water bill payers.
For its part, the Environment Agency confirmed it is monitoring the site through “rigorous environmental assessments.” The agency previously blocked a similar proposal in 2019, citing the unacceptable environmental impact of discharging massive quantities of treated effluent into the Thames. As the debate intensifies, critics point out the irony of the scheme’s output: the 75 million litres of water the plant aims to recycle daily is only a fraction of the 571 million litres Thames Water currently loses to leakage every day.
