Levels of a toxic 'forever chemical' rose to 13 times the legal limit during Thames Water pilots for a controversial multimillion-pound water recycling scheme that would pump millions of litres of treated sewage into the River Thames during drought, according to exclusive data obtained by The Guardian. The findings directly contradict the utility's public assurances that the project will not harm the riverine environment.
The pilot data, obtained by The Guardian, reveals that concentrations of perfluoroalkyl and polyfluoroalkyl substances (PFAS) — known as 'forever chemicals' because they do not break down in the environment — surged dramatically during Thames Water's test runs of the proposed recycling system. The scheme is designed to draw off tens of millions of litres of water a day from the River Thames during drought conditions and replace it with treated effluent from sewage treatment plants.
Thames Water has publicly stated that the water recycling project in south-west London 'will not harm the riverine environment', but the pilot results suggest otherwise. The spike in PFAS levels to 13 times the legal limit during the test phase raises serious questions about the safety of the proposal and the adequacy of the treatment processes being considered.
The company has described the scheme as a critical part of London's drought resilience plan, given the increasing frequency of dry spells driven by climate change and population growth. However, environmental groups and local communities have long opposed the plan, warning that pumping treated sewage into a major river could introduce a cocktail of pollutants, including pharmaceuticals, microplastics, and PFAS.
PFAS have been linked to a range of health problems, including cancer, liver damage, and immune system disruption. The legal limit for PFAS in drinking water in the UK is set by the Drinking Water Inspectorate, but treated sewage discharged into rivers is subject to different environmental quality standards. The pilot data suggests that even with advanced treatment, the recycling process may not be sufficient to remove these persistent chemicals to safe levels.
Thames Water has not yet responded to the specific pilot findings, but the company's previous statements have emphasised the need for water recycling to secure London's water supply. The utility is under pressure from regulators to reduce water leakage and invest in infrastructure, but the PFAS spike adds a new dimension to the controversy.
The Environment Agency, which regulates water quality in England, is expected to review the pilot data as part of its assessment of the scheme. Environmental campaigners are calling for an independent investigation and a halt to the project until the risks are fully understood.
Analysis
Why This Matters
- The PFAS spike directly threatens the safety of London's drinking water supply, as the River Thames is a source of drinking water for millions downstream.
- The scheme is set to become a test case for water recycling in the UK, with broader implications for how utilities manage drought without compromising environmental health.
- If approved, the project could set a precedent for similar schemes in other water-stressed regions, making the outcome of this regulatory review critical.
Background
Thames Water has been grappling with a combination of aging infrastructure, high leakage rates, and increasing drought risk. The water recycling scheme was proposed as a way to augment flows in the River Thames during dry periods, allowing the company to continue abstracting water for London's supply. The concept of augmenting rivers with treated sewage, known as 'indirect potable reuse', is already used in parts of the US and Australia, but it remains controversial in the UK due to public perception and ecological concerns.
PFAS have been used for decades in industrial and consumer products, and they have accumulated in the environment, including in sewage. Even advanced treatment processes like reverse osmosis can struggle to remove some PFAS compounds. The legal limit for PFAS in drinking water is set at 0.1 micrograms per litre for individual compounds, but multiple PFAS are often present together, increasing the risk.
Key Perspectives
Thames Water: The utility argues that the project is essential for drought resilience and that the pilot data is preliminary. They maintain that the final treatment process will be designed to meet all regulatory standards, and that the public should trust the company's engineering and environmental safeguards.
Environmental groups and local communities: Groups such as the London Rivers Action Plan and local residents' associations oppose the scheme, warning that the pilot data confirms their worst fears. They argue that the risk of PFAS and other contaminants is too high, and that Thames Water should focus on reducing leakage and demand management instead.
Regulators (Environment Agency, Drinking Water Inspectorate): Regulators are expected to scrutinise the pilot data closely. They must balance the need for drought resilience with the legal requirement to protect aquatic ecosystems and public health. The spike to 13 times the legal limit could trigger a requirement for a more comprehensive environmental impact assessment or a redesign of the treatment process.
What to Watch
- The Environment Agency's formal response to the pilot data and any request for an independent review.
- Thames Water's next public consultation and whether the company revises its treatment plans or offers additional safeguards.
- The outcome of the wider regulatory review of PFAS in the UK, which could lead to stricter limits on discharges into rivers.
- Any legal challenges or protests from environmental groups that could delay or block the project.