How often do storm overflows spill sewage?
Storm overflows in England spilled 292,119 times in 2025, for a total of 1.88m hours, according to the Environment Agency. That is 20.5 spills per overflow on average.
Spill events in 2025. down 35% on 2024.
Hours of spills in 2025. down 48% on 2024.
Average spills from each overflow, 2025.
Spills since monitoring began
What’s this?
The number of times storm overflows released untreated or partly treated sewage and rainwater into rivers and seas in England, as counted by monitors.
What it cannot tell you: Only overflows fitted with a working monitor are counted, and nearly all are monitored only since 2020, so the years before are not comparable. Spills depend heavily on how much it rained.
What’s this?
The total time storm overflows spent releasing sewage and rainwater, added up across all overflows.
What it cannot tell you: Only overflows fitted with a working monitor are counted, and nearly all are monitored only since 2020, so the years before are not comparable. Spills depend heavily on how much it rained.
What’s this?
The average number of spills from each overflow with usable monitor data.
What it cannot tell you: Only overflows fitted with a working monitor are counted, and nearly all are monitored only since 2020, so the years before are not comparable. Spills depend heavily on how much it rained.
What’s this?
The number of storm overflows in England with usable monitoring data that year.
What it cannot tell you: It rises as more overflows are fitted with monitors, which is why early years show fewer spills.
Year by year
England, calendar years, from the water companies' annual returns.
| Period | Sewage spills from storm overflows, England | Hours of sewage spills, England | Spills per storm overflow | Storm overflows with monitor data |
|---|---|---|---|---|
| 2025 | 292,119 | 1.88m | 20.5 | 14,239 |
| 2024 | 450,398 | 3.61m | 31.8 | 14,182 |
| 2023 | 464,056 | 3.61m | 33.1 | 14,031 |
| 2022 | 301,091 | 1.75m | 23.0 | 13,080 |
| 2021 | 372,533 | 2.67m | 29.4 | 12,393 |
| 2020 | 403,375 | 3.10m | 32.6 | 12,092 |
Questions people ask
What is a storm overflow?
A relief valve on the sewer network. In heavy rain, when pipes would otherwise back up into homes and streets, the overflow lets a mix of rainwater and sewage out into a river or the sea.
Does a higher count mean the problem got worse?
Not by itself. Monitors were fitted to most overflows only by 2023, and the number of spills depends heavily on how much it rained that year, which is why we show the years from 2020.
Who collects this?
Water companies must monitor their overflows and report the figures to the Environment Agency, which publishes them each year.
What does “sewage spills from storm overflows, england” measure?
The number of times storm overflows released untreated or partly treated sewage and rainwater into rivers and seas in England, as counted by monitors. It was 292,119 (spill events in the year) in 2025, down 28% on 2020. The highest we have is 464,056 (2023) and the lowest 292,119 (2025).
What does “hours of sewage spills, england” measure?
The total time storm overflows spent releasing sewage and rainwater, added up across all overflows. It was 1.88m (million hours in the year) in 2025, down 39% on 2020. The highest we have is 3.61m (2023) and the lowest 1.75m (2022).
What does “spills per storm overflow” measure?
The average number of spills from each overflow with usable monitor data. It was 20.5 (spills per overflow in the year) in 2025, down 37% on 2020. The highest we have is 33.1 (2023) and the lowest 20.5 (2025).
What does “storm overflows with monitor data” measure?
The number of storm overflows in England with usable monitoring data that year. It was 14,239 (overflows) in 2025, up 18% on 2020. The highest we have is 14,239 (2025) and the lowest 12,092 (2020).
Sources: Environment Agency, storm overflow event duration monitoring (annual returns). Updated every night. Each chart has a CSV and a Share button.
See also: Water bills