Thames Water Utilities Limited supplies water and sewerage services to London and the Thames Valley.
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The Environment Agency rated Thames Water 1 star ('poor performing company') for 2024, and in 2025 Ofwat imposed a record £122.7m penalty. In 2025/26 it had 24 serious pollution incidents, discharge permit compliance of 88.22% and average leakage of 573.7 Ml/d. No third-party assurance of its greenhouse gas figures was found. Its zero market-based Scope 2 relies on supplier renewable electricity, and its reported Scope 3 covers operational categories only, with no capital carbon.
Thames Water scores 36/100 (Below expectations) on SINK's independent climate assessment, scored from public data only. Fees pay for the review, never the result. Last verified October 2026.
That places Thames Water joint 459th of 847 companies scored, and 11th of 11 in Water & Sewerage.
Thames Water sits at the bottom of the water & sewerage pack.
Among the 11 major water & sewerage brands we've scored, Thames Water sits 11th of 11.
Its three lowest-scoring questions, and what the evidence didn't show.
Event-duration monitoring and 15.1% three-year leakage reduction do not offset scale of pollution.
Ofwat imposed record £122.7m penalty (£104.5m for wastewater), finding Thames Water 'failed to protect the environment'.
Scope 1 rose in 2024/25: wastewater 215.9 to 220.2 kt, water 8.8 to 9.7 kt.
A score changes when the evidence does. We use new published evidence at the next rescore. Evidence that isn't public can count through an evidence review.
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Get in touch →Strongest on Carbon Footprint — Operations and Energy Source (6/10, 6/10). Weakest on Water Impact and Controversies & Red Flags (1/10, 2/10).
The 3 companies in the sector scoring nearest above Thames Water.
Yorkshire Water's market-based emissions rose from 281 to 295 ktCO2e between FY2024 and FY2025, and Scope 1 rose from 85 to 88 kt.
See the breakdown →Southern Water's gross Scope 1 and 2 emissions were flat between 2022–23 and 2024–25 (152,364 t to 152,320 t, location-based), and its Scope 3 rose about 35% year on year.
See the breakdown →Dŵr Cymru Welsh Water's total market-based emissions rose 9% to 443.4 kt in 2025/26, and its emissions targets are under review.
See the breakdown →The formula and all 9 sources.
Same ten questions for every company. No private weighting.
SINK = (0.3 × Base + 0.7 × Performance) × Scale9 sources used in this assessment. All publicly available. Each row shows which of the ten questions it informed.
“In 2025/26 the water sector, in agreement with industry regulator Ofwat, has adopted an updated emissions factor for nitrous oxide”
“Includes fossil fuels, site process and fugitive emissions and vehicle transport (Fleet).”
“In 2024/25 we self-generated and used 475.3GWh of renewable energy, covering 25.8% of our own energy needs.”
“RWE will supply a total of 132 gigawatt hours (GWh) of clean electricity annually”
“33 serious incidents – this is rated as red”
“Thames Water has been fined £122.7 million after two investigations into wastewater and dividend payments, in the largest penalty Ofwat has ever issued”
If you believe a source has been misread or a newer version exists, submit a challenge.
Thames Water Utilities Limited supplies water and sewerage services to London and the Thames Valley. It was formed on privatisation in 1989 and is headquartered in Reading. Its filed accounts for the year to 31 March 2026 report revenue of £3,756.5m, including £140.9m passed through for the Thames Tideway Tunnel, and an average of 8,472 permanent employees. It is regulated by Ofwat and the Environment Agency.
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