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. 


Action on Storm Overflows 

In response to the changing expectations of our customers, we are investing more than ever to reduce storm overflow spills, reduce 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, watercourses 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 £1 billion will be spent on storm overflow monitoring and improvements, while our total enhancement spend on the environment will double to £4 billion. You can read our full business plan here.


This builds on our current Water Industry National Environment Programme (WINEP), being delivered through to 2025, which will see £10.7 million invested to reduce spills at 11 of our highest priority sites, bringing average spills down in line with our long-term aspirations.  


Our current WINEP is one of the biggest environmental programmes in the water industry. Since 2020, we’ve made £200 million 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.


As part of our Get River Positive commitment, we've pledged to ensure storm overflows and sewage treatment works do not harm rivers. We’ve also committed to be as transparent as possible with the data we collect about our water recycling network and the improvements that we're making, especially around storm overflows.


What are storm overflows?

Throughout this Asset Management Plan (AMP7) period, which runs from 2020 to 2025, we’ve already made improvements to the way we operate and reduce storm overflows.  


Central to this has been the introduction of Event Duration Monitors (EDMs), which measure how often and for how long storm overflows discharge into the environment. EDMs ensure we have the data and insight needed to address and reduce storm overflows discharging across our network.  


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


Targeted improvements through the use of EDM monitors has mitigated the impact of heavy rainfall despite an increase in storm overesulted in a reduction in the use of storm overflows across our region.  


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. However, it is important to acknowledge the exceptionally wet weather we had in 2023, particularly late in the period, which meant that 70% of our spills were in Q4 alone and in stark comparison to the extremely dry year in 2021, as climate change continues to result in more extreme weather events.


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


This year we’ve pledged an additional £50 million to tackle even more storm spills and we’re investing at pace to deliver our Pollution Incident Reduction Plan.


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


Year-on-year data changes

Storm Overflow Action Plan Data