How much sewage do English water companies spill, and what does the monitoring data show?
Every storm overflow in England now has a monitor, and the numbers swing with the weather.
Guess first
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In 2025, in England spilled 291,492 times, a 35% reduction on 2024, and total monitored spill duration fell by 48%. The numbers swing mainly with the weather. The has data from every overflow because record when storm overflows discharge and how long each discharge lasts.
The picture over the years is not a straight line. The average number of spills per overflow was 32.6 in 2020, 23 in 2022, 33.1 in 2023, 31.8 in 2024 and 20.5 in 2025. Rainfall is the primary driver of storm overflow spills, because surface water run-off can put pressure on England's combined sewer network. The says much of the 2025 improvement reflects unusually dry conditions following a particularly wet 2024.
There is another catch. With just 7% of fitted with a monitor in 2010, and now every one fitted, the says that increased installation of monitors makes direct comparisons of spill data over time very difficult.
The official reading is mixed. When the 2025 figures came out in March 2026, Water Minister Emma Hardy said spills were down on the previous year, but that there is still an unacceptable amount of sewage entering waterways. The 's own conclusion is that it needs sustained maintenance and investment in drainage networks.
Try it
Overflows times average spills
y = 14.2x + 0
Challenge · With about 14.2 thousand overflows, what average gets you to roughly 290 thousand spill events, as in 2025?
Quiz me
0/3
Recap
Spill counts follow the rain, and more monitors means more counted, so compare years carefully.
💡 A trick to remember it · Rain, meters, upgrades: read every spill number with those three in mind.
Surprising fact · Average spills per overflow were 20.5 in 2025 against 31.8 in 2024, a fall the regulator attributes largely to a dry year.
Connects to
- 🚽 How does a sewage treatment works clean the water you flush away?
- 🌧️ What is a combined sewer and why do storm overflows dump sewage into rivers?
- 🏭 Why was England's water privatised in 1989, and what has changed since?
- 🚇 How did Brunel's iron shield let miners dig under the Thames when engineers said it was impossible?
- ✈️ Why would armoring a bomber's most-hit spots be a mistake?
Sources (4)
No source, no claim. Every fact in this lesson (16 claims) cites at least one of these.
- [1]Fewer and shorter storm overflow spills in 2025, new monitoring data shows (26 March 2026) · GOV.UK (Environment Agency)
- [2]Environment Agency storm overflow spill data for 2024 (27 March 2025) · GOV.UK (Environment Agency)
- [3]Environment Agency publishes storm overflow spill data for 2023 · GOV.UK (Environment Agency)
- [4]Government initial response to Independent Water Commission's final report (21 July 2025) · GOV.UK