‘Forever chemicals’ surge during pilot of Thames Water plan to combat drought
Thames Water’s trial of a proposed drought-resilience scheme reportedly caused levels of the persistent pollutant PFOS to exceed the legal surface-water limit by up to 13 times. The findings raise questions about whether the £350m-plus project can protect the River Thames while supplying extra water during drought, despite the company’s public assurances that it would not harm the environment.
The plan would take up to 75 million litres a day from the Thames at Teddington and replace it with treated wastewater from Mogden via a new tunnel. Pilot results recorded PFOS at 6.3 and 8.7 nanograms per litre, against a legal limit of 0.65, and also identified high iron levels; Thames Water said compliance would be operationally difficult and costly. The project’s expected cost has risen above £500m, while the company reportedly leaks 571 million litres of water daily and carries about £20bn of debt.
- Pilot tests found PFOS up to 13 times the legal limit.
- The drought scheme would add treated wastewater to the Thames.
- Compliance may require costly, frequent filtration work.
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Thames Water supplies water and wastewater services across much of south-east England. During droughts, water companies may need extra sources of supply, but taking and returning water can affect rivers and wildlife.
The proposed scheme would take water from the Thames near Teddington and send treated wastewater from Mogden into the river through a new tunnel. PFOS is a long-lasting chemical that can persist in the environment; rules set limits for pollutants in surface water.
The project is part of a wider debate about how to secure water supplies while protecting rivers and keeping costs manageable. Thames Water’s finances, leakage and the scheme’s rising price are relevant to questions about how it could be funded and delivered.
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The case for
England's south-east faces serious water scarcity, and major infrastructure investment is essential for drought resilience and meeting population needs. Pilot programmes routinely identify technical challenges that can be engineered or mitigated; contamination levels and iron content represent operational issues rather than fundamental design problems. Water recycling from treated wastewater is established practice globally, and pursuing solutions to achieve environmental compliance would deliver critical infrastructure that cannot be foregone because development encounters difficulties.
The case against
PFOS is a highly persistent chemical that accumulates in the environment and organisms over time, and legal limits exist to protect human and environmental health. The scheme would release pollutants into the Thames at 6-13 times the legal limit, posing genuine risks to aquatic life and drinking water supplies serving millions of people. Thames Water's £20bn debt, inability to prevent massive daily leaks, and environmental track record raise serious doubts about the company's capacity to operate complex infrastructure reliably and maintain environmental compliance, particularly as costs continue rising.