Thames Water
Monitored storm overflows run by Thames Water spilled 9,189 times in 2025, according to the Environment Agency's annual returns. That is down 38% from 14,713 in 2021.
Those spills lasted a combined 107,822 hours in 2025. That is down 34% from 163,090 hours in 2021.
In 2024, the Environment Agency recorded 43.0 pollution incidents per 10,000 km of sewer for Thames Water.
Of the years from 2021 to 2025 in the Environment Agency's returns, Thames Water reported its largest number of monitored spills in 2024 (23,061).
Storm overflows
Storm overflow spills (monitored)
| 2021 | 14,713 |
| 2022 | 8,014 |
| 2023 | 16,990 |
| 2024 | 23,061 |
| 2025 | 9,189 |
Hours of storm overflow spills
| 2021 | 163,090 hours |
| 2022 | 74,693 hours |
| 2023 | 196,414 hours |
| 2024 | 298,081 hours |
| 2025 | 107,822 hours |
Average spills per storm overflow
| 2021 | 31.9 |
| 2022 | 17.0 |
| 2023 | 27.9 |
| 2024 | 39.4 |
| 2025 | 15.9 |
Average length of a spill
| 2021 | 11.1 hours |
| 2022 | 9.3 hours |
| 2023 | 11.6 hours |
| 2024 | 12.9 hours |
| 2025 | 11.7 hours |
Storm overflows with spill data
| 2021 | 461 |
| 2022 | 472 |
| 2023 | 610 |
| 2024 | 585 |
| 2025 | 579 |
Environmental Performance Assessment
Where Thames Water sits in the ladder of power
The bodies above Thames Water and the council areas it serves. How the ten levels work.
Level 4: County councils, combined authorities and metro mayors
- Thames Water this page
Level 6: National government
- Department for Environment, Food and Rural Affairs the UK government department responsible in England
- UK government and Parliament
Level 7: Regional blocs and supranational bodies
- Council of Europe and the European Court of Human Rights (CoE / ECtHR) The UK Government says the United Kingdom was one of the Council of Europe's founding members.
Level 8: The UN and global treaty bodies
- United Nations (General Assembly and Security Council) The UN lists the United Kingdom as a member admitted on 24 October 1945.
- United Nations Security Council (UNSC) The UK is one of the five permanent members of the Security Council and holds the veto, according to the UN.
- NATO NATO lists the United Kingdom among its 12 founding members, which signed the North Atlantic Treaty in Washington, D.C.
- World Health Organization (WHO) WHO's list of member states includes the United Kingdom of Great Britain and Northern Ireland.
- World Trade Organization (WTO) The WTO says the United Kingdom has been a WTO member since 1 January 1995 and a member of GATT since 1 January 1948.
- Commonwealth of Nations The UK is one of the 56 members, one of three European members with Cyprus and Malta, and the Commonwealth Secretariat is headquartered at Marlborough House in London.
Level 9: The IMF, World Bank and global finance
- International Monetary Fund (IMF) The UK has been a member since 27 December 1945 and has a quota of SDR 20,155.1 million (IMF country page for the United Kingdom).
- World Bank Group (WBG) The UK holds 3.75% of voting power in the IBRD (data as of 30 June 2026) and 6.92% in IDA (as of 30 June 2026), according to the World Bank's voting tables.
Level 10: G7, G20, Davos and global forums
Sources
- Environment Agency, Event Duration Monitoring storm overflow annual returns, read 15 October 2026, SHA-256
9edde3a2c5052b5e… - Environment Agency, environmental performance assessment, read 15 October 2026, SHA-256
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Water and sewerage companies · how these figures are presented · built 15 October 2026