What is a storm overflow?
Storm overflows are designed to keep wastewater out of the sewers and, at times, people's homes.
When there’s heavy rain the sewer system can get overwhelmed – causing wastewater to back up.
To stop that from happening, our systems automatically redirect extra stormwater into our 2,190 storm overflows, which let it flow out into nearby watercourses.
We know these overflows are used more than anyone would like, and we’re working hard to change that. That's why we’re investing £1.5 billion into smarter, more sustainable ways to cut down how often they’re needed and help protect the environment.
What's the issue?
The sewer network and demands upon it have changed dramatically since it was built:
* more wastewater being created
+ climate change bringing more heavy rainfall
= up to 30 times more wastewater in the pipes.
This creates extra system pressure and puts more homes at risk of wastewater flooding.
What are we doing?
Investing £1.5 billion into more sustainable engineering solutions including:
- surface water sewers
- underground storage tanks
- nature-based solutions
- sustainable drainage systems.
How can you help?
A few small changes to make a massive difference:
- using a water butt
- only flushing the 3 P's: poo, pee and paper.
This will ensure less water and less blockages end up in the system.
See how we're doing
We publish figures on our storm overflow use monthly. We share these with the Environment Agency yearly but you can look anytime.
Check live map
We have created a live map where you can see what, if any, storm overflows are in operation across the county in real time.
Watch the video
Find out how storm overflows prevent wastewater backing up into people's homes during heavy downpours.
Any questions?
How do you monitor storm overflows?
Our storm overflows are highly regulated with permits provided by the Environment Agency which set out the conditions for when an overflow can operate and how it should be configured.
We closely monitor how our overflows are performing and we report any activity that goes outside of the permit conditions to the Environment Agency, who then investigate.
There are two ways you can view data on our storm overflows
Our interactive map that shows in near real-time whether our storm overflows are operating
Our annual storm overflow data. Every month we publish our individual discharge events. We collate all this data and publish it on our website annually after sharing it with the Environment Agency. We have a dedicated data page where you can look through the data and read the summary results.
Can you explain more about the different types of storm overflow?
Surface water sewers
Divert rainwater into a dedicated sewer, which is separate to the combined sewer to reduce strain on the sewer network. This helps prevent the wastewater network from becoming overwhelmed during periods of bad weather and means that rainwater can be redirected back into waterways without having to go through our wastewater treatment process.
Underground storage tanks
Can store excess wastewater, meaning when there’s heavy rainfall, we’ll be able to hold more excess wastewater back and reduce reliance on storm overflows during periods of bad weather.
Nature-based solutions
Include full treatment and phosphorous-specific wetlands. These wetlands are made up from a number of interconnected ponds filled with a variety of wetland plants that naturally treat wastewater by removing pollutants.
Phosphorus wetlands go a step further, using specific plants that can absorb and break down phosphorus, helping to filter wastewater in a sustainable and low-carbon way while also providing a habitat for wildlife to thrive.
Once the water is treated it drains back into a local watercourse, removing excess strain from the sewer network.
Sustainable drainage systems
Include permeable flooring, swales and rain gardens. These sustainable drainage systems help slow the flow of rainwater in built-up areas where concrete and tarmac dominate.
Because these hard surfaces don’t absorb water, rain runs off into drains, which can put extra pressure on the sewer network. These sustainable drainage system solutions ease that strain by capturing rainwater in a more natural, sustainable, and low-carbon way.