Spill durations
How long storm overflow spills lasted in 2024 and 2025, from the water companies' monitor records published by the Environment Agency. A record of the past, not a forecast.
Company by company
Each company's spills in 2024 and 2025: the typical spill (half were shorter, half longer), the long end (one spill in ten lasted longer), and how many lasted over 6 and over 24 hours. Companies do not record spills the same way: United Utilities changed how it records them in 2026, and typical lengths differ several-fold between companies. So a difference between two companies may be in the recording, not in the overflows.
Spills already running
How often a spill that had already run some hours was still running some hours later, across each company's overflows in 2024 and 2025. Every whole hour a spill was running, in its first 72 hours, is one hour checked. Each figure is the share of those hours at which the spill was still running that many hours on, and the hours checked are the count behind it.
These figures describe 2024 and 2025. They are not a forecast: they do not say when any spill will end, here or anywhere.
A spot's overflows
Pick a spot to see how long the spills lasted at each storm overflow upstream of it, in 2024 and 2025. Each spot's overflow history page has the same figures, under each year's annual return.
- Typical spill
- Half of the overflow's spills in those years were shorter, half longer.
- Long end
- One spill in ten lasted longer than this.
- Longest
- Its longest spill in the two years.
- Spills
- The monitor's events, joined into one spill when they overlap or one starts less than an hour after the last ended. So the counts differ from the annual returns', which count by the Environment Agency's 12/24 method.
- Few spills
- Fewer than 5 spills in the two years, so its typical length rests on little.
- No row
- No recorded spill in those years, or no record. That is not the same as no spills: the annual returns on the overflow history page give each year's count.
What these records do not say
- a forecast of when a spill will end
- the volume or strength of a discharge
- that a short spill was harmless
- that companies record events the same way
For what the overflows upstream of a spot are doing now, and the forecast, see the spot's own page.
How the figures are made
From each company's storm overflow start and stop records for 2024 and 2025, as the Environment Agency publishes them. An overflow's events are joined into one spill when they overlap or one starts less than an hour after the last ended. An overflow with no recorded spill in those years, or with no record, is not in them. Nine English companies are in them; Dŵr Cymru Welsh Water is not.
Sources
Environment Agency, storm overflow EDM start/stop data 2024 and 2025, Open Government Licence v3.0. Joined into spills and summarised by SwimSignal. Data credits.