During pilot tests of Thames Water’s controversial multimillion‑pound water‑recycling project, concentrations of a toxic “forever chemical” rose to 13 times the legal limit.
The findings clash with the utility’s public assurances that the scheme would not damage the riverine environment.
Internal technical notes obtained by the Guardian reveal that the recycling system quickly and markedly increased levels of perfluorooctane sulfonate (PFOS), a suspected carcinogen, exceeding the limit by as much as thirteenfold.
Standard wastewater treatment does not remove or break down PFAS (per‑ and polyfluoroalkyl substances), which persist in the environment and have been linked to widespread river contamination and potential health risks. Recent data indicate that every English water body now contains detectable levels of these chemicals.
Thames Water’s recycling initiative aims to alleviate future water shortages driven by population growth and climate‑induced droughts by abstracting up to 75 million litres of river water per day at Teddington during low‑flow periods and replacing it with an equivalent volume of treated sewage from the Mogden works via a new tunnel.
The 75 million‑litre daily abstraction represents only a fraction of the 571 million litres the company loses each day through leakage.
However, the pilot results suggest that the volume of treated effluent would make it extremely difficult for the river to meet existing standards for PFAS and pesticides.
Despite seeking a development consent order for the £350 million scheme (now projected to exceed £500 million), Thames Water has maintained publicly that the recycling system will not harm the river, its habitats, or public health.
The technical notes show PFOS concentrations of 6.3 nanograms per litre in the first test and 8.7 nanograms per litre in the second, while the UK legal limit for surface waters is 0.65 nanograms per litre.
The documents note a “rapid breakthrough” of PFOS above the threshold within less than one month of operation, stating that staying within legal limits would be “operationally challenging” and would necessitate frequent regeneration, reactivation, and replacement of carbon filters, incurring significant additional costs.
Besides PFOS, the pilots revealed elevated iron levels in the treated water, which the notes warn could have a “significant detrimental impact” on the river.
Ian McNuff of the campaign group Solar, which opposes the project over fears of irreversible environmental damage, remarked: “Thames Water described the pilot results as ‘operationally’ challenging.
“In short, they cannot make it work properly. The test failures were swift, and the notion that they could toggle this system on and off as a reliable drought asset is unrealistic given current standards, let alone the stricter limits expected for PFAS and pesticides.”
Costs for the recycling scheme are already climbing for Thames Water, which is grappling with £20 billion of debt and faces the prospect of government‑administered administration.
The original £350 million budget is now expected to surpass £500 million after the utility discovered it must install additional mechanical pumps within a nature reserve near Teddington to move the water, according to project insiders.
The Environment Agency has received the pilot results. The agency previously rejected a similar proposal in 2019 due to the unacceptable environmental impact of discharging millions of litres of treated effluent into the river.
The project also faces opposition from the local council and local MPs, including Liberal Democrat MP Munira Wilson. Nevertheless, as a nationally significant infrastructure project, it can proceed without local consent.
An Environment Agency spokesperson stated:
“We have strict legal requirements in place to protect our rivers, groundwater and drinking water catchments from toxic chemicals and the Teddington site will continue to undergo rigorous environmental assessments to ensure these conditions are met before any development work can begin.”
“Environmental protection and sustainable development must go hand‑in‑hand and water recycling projects, combined with new reservoirs, will be critical to securing future water supplies effectively.”
A Thames Water spokesperson added:
“The Teddington Direct River Abstraction (TDRA) project will not be allowed to operate without securing an environmental permit from the Environment Agency.”
“The pilot plant study was designed to test a range of technologies to inform and refine the final design of the tertiary treatment plant. The data from the pilot plant study are not indicative of what would be discharged back into the river once the project is fully operational.”
The spokesperson continued:
“We want to see PFAS banned and the development of a national plan to remove it from the environment, which should be funded by manufacturers rather than water‑bill payers.”
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