Monitored storm overflows in England spilled sewage 20.5 times each on average in 2025: 292,119 spills from 14,239 overflows
Monitored spill events from storm overflows: average per overflow with spill data, number of overflows with spill data, total spills and their total duration, England, 2016 to 2025. Spills per overflow, overflows, spills and million hours.
Latest figures
| Series | Period | Value |
|---|---|---|
| Average spills per monitored overflow | 2025 | 20.5 |
| Storm overflows monitored | 2025 | 14,239 |
| Total spill events | 2025 | 292,119 |
| Total duration of spills | 2025 | 1.88 |
Notes
- Monitoring coverage rose sharply, from 862 storm overflows returning spill data in 2016 to 14,239 in 2025. Totals for years when fewer overflows were monitored leave out spills from the rest, so they aren't comparable with later years.
- The average is spill events divided by the number of overflows with spill data that year. It allows for the number monitored, but not for which ones: in years when few overflows were monitored, the ones that were may not be typical of all of them.
- The Environment Agency's long-term trends table gives a different average in some years (32.6 in 2020, 29.4 in 2021). This chart divides the published totals instead, so the average matches the other panels.
- From 2021, companies were asked to list every storm overflow they operate, whether or not a monitor was fitted (14,303 in 2025). Overflows with a monitor fitted but no reliable data for the year are not counted as monitored.
- Spills are measured by event duration monitors fitted to each overflow, and counted by the 12/24 hour method: the first 12 hours of a discharge count as one spill, then each 24-hour block after that with any discharge counts as one more, until a 24-hour block with none.
- Figures are for England only, and include Dŵr Cymru Welsh Water's overflows in England. Storm overflows are designed to release diluted sewage into rivers and the sea when heavy rain would otherwise overwhelm the sewers, so the number of spills depends partly on how much rain fell that year.
Sources
More on climate
- Fine particles (PM2.5) averaged 8.0 µg/m³ at urban background sites in the UK in 2025, and nitrogen dioxide 20.4 µg/m³ at roadside sites in 2025
- UK greenhouse gas emissions were 367 million tonnes in 2025, 54% lower than in 1990
- Low-carbon sources generated 64.3% of UK electricity in 2025, renewables 52.1% and fossil fuels 32.3%
- England's recycling rate for waste from households was 43.8% in 2024
- Storm overflows run by South West Water spilled 34.0 times each on average in 2025, and those run by Anglian Water 12.0 times