Storm overflows

Storm overflows are outlets from main sewer systems that allow excess rainwater into rivers and seas to protect people’s homes from flooding during periods of heavy or prolonged rainfall or snow melt. They’ve been in place for many years.

In response to the changing expectations of our customers, we are investing more than ever to reduce storm overflow spills and pollutions and restore river health. We recognise customers want us to take swift action to end storm overflow discharges. We intend to meet these expectations and have geared our latest Business Plan to address the highest priority overflows soonest. Our Storm Overflow Action plan outlines how we’ll improve all storm overflows ahead of the government’s 2050 deadline. You can read our summary here or visit Water UK’s interactive dashboard to find the information on individual sites.

To determine the priority overflows for the next five years, a thorough prioritisation process was carried out using criteria defined by Defra and the Environment Agency. This was used alongside feedback from stakeholders and considers current discharge frequency and impact, watercourse types - prioritising chalk streams, and areas known for wild swimming to create a weighted prioritisation matrix.

This process took place with input from the Environment Agency, Natural England and the Rivers Trusts, who collectively agreed the prioritised storm overflows to receive investment as part of our Business Plan for 2025 to 2030. This programme of work will deliver against the legal obligations of the Environment Act and address feedback from our local partners.

To do this, we have proposed a significant package of investment between 2025 and 2030. Approximately £1billion will be spent on storm overflow monitoring and improvements, while our total enhancement spend on the environment will double to £4billion. You can read our full business plan here.

Since 2020, we’ve made £200million of direct investment in reducing overflow discharges by increasing storm storage capacity and increasing flow volume passed on to our water recycling centres, with more than 300 of our schemes completed early.

What are storm overflows?

We have full EDM coverage of storm overflows across our network and have surrendered permits for 340 storm overflows since privatisation as they are no longer used, representing approximately 16% of all overflows in our network.

Our EDM monitors and investments are helping reduce spills and have moved the dial in the right direction. Spills would have been considerably higher without it.

While it is important to acknowledge the exceptionally wet weather we had in 2023 and 2024 we know that our assets need to be resilient to changing weather patterns and we have to find better ways of dealing with extreme rainfall.

Our next five-year business plan builds at pace on the work we've already started. It contains our largest ever investment - £1billion - into tackling storm spills, and £11billion overall into improving our performance. We've prioritised this work to deliver the biggest benefits first, because we recognise and share the desire of our customers, to get on with addressing this issue.

We’re going even further, investing to make storm overflows a relic of the past.

Want to know more? Click here for our Frequently Asked Questions about Storm Overflows.

Year-on-year data changes

Description	2023	2022	2021	2020
Number of Event Duration Monitors (EDMs)	1431	1058	834	703
Total number of spills	31,395	16,082	21,351	17,385
Total duration of spills (hours)	273,317	89,514	194,594	170,325
Average ‘spill’ activation per EDM	22	15	26	25
Average duration of spills per EDM (hours)	190	85	233	242
Average hours per spill event	8.6	5.6	9.1	9.8
Rainfall total (mm)	858.32	577.51	677.97	738.70