Information about storm discharge
If you have questions about storm discharge and how it impacts our rivers, you should find the answer below. If not, you can contact us using our online form.
Why are there storm discharges when there hasn't been a storm?
Heavy rainfall can have an instant impact on our sewer systems but larger catchments have a slower response. This means there can be a delay between it raining and the flow arriving at the overflow point.
Also, groundwater levels rise in the winter months, leading to more water ending up in our sewers. This means discharges can happen after a relatively small storm. We've been developing groundwater impacted system management plans to tackle this issue.
How much sewage have you discharged in the river?
Our EDM monitors only measure the start and stop times of storm discharges. We don't hold data on storm discharge volumes.
My local storm overflow has been discharging for multiple days; what are you doing about it?
When it rains, the excess surface water finds its way to the sewerage network. Heavy or continued rain can risk overwhelming it. Where the sewer network covers a large area, it takes a while for the water to drain through and for storm tanks to be emptied for treatment.
Our team is committed to protecting the environment. We work hard every day to ensure wastewater is properly treated before it's discharged into our rivers and streams. We use EDM data, along with other tools and information, to identify and respond to problems.
Can you put up signs following a discharge?
We're committed to sharing information as close to real time as possible through our storm discharge map.
What's the impact of storm discharge on the environment?
Untreated sewage has the potential to cause significant harm to the environment. We know our wastewater activities impact this, as well as your enjoyment of our rivers and other watercourses.
In most cases, storm discharges are heavily diluted by rainwater. So, although they're unpleasant, their impact to river water is likely to be minimal. The Environment Agency reports that, overall, they do less damage to the environment than other sources of pollution.
The impact of each location and discharge will vary. Our storm discharge map only gives information on the status of our storm overflows. It shouldn't be used to determine water quality or if it’s safe to enter the water. This is because many different factors affect the water quality and safety of our rivers.
If you'd like to find out more about river water quality, and water quality sampling in your area, contact the Environment Agency. You can find their water quality data archive here. You can also find out about your local river catchment partnership here.
Is there a health risk to entering water that may have received a sewage discharge from an overflow?
We appreciate how much our waterways are loved and we want you to be able to enjoy them. Our near real-time storm discharge map can help you make more informed decisions but it doesn't tell the full story of river water quality.
There are other potential hazards in watercourses. These include runoff from farming, industry and roads, and bacteria and parasites from livestock and other animals. This is why we support the government’s advice on open water swimming.
How long after a storm discharge can I enter the water?
Please remember to consider all the safety factors when wild swimming in rivers and other watercourses. It can take up to 4 days for the sewage to clear after a storm discharge. You should also bear in mind that the data provided from our EDM monitors isn't always accurate. We're sharing it so you can make more informed decisions.
Our map only indicates our storm overflow activity, not the other potential hazards in watercourses. With so many different factors affecting the water quality and safety of our watercourses, our data should not be used to determine if it’s safe to enter the water. See the government’s advice on open water swimming.
Do you test the river water regularly?
The Environment Agency (EA) is responsible for testing river quality.
If we think we've polluted a watercourse, we'll test the water quality and work with the EA accordingly. Find out more about reporting pollution.
What are you doing to avoid having to use storm overflows?
We're spending £1.25 billion on maintaining and improving our operational sites between 2020 and 2025. That's an average of £250 million a year. We've committed to reducing the total duration of storm overflow activity in our region by 50% (80% in sensitive catchments) by 2030. We'll be working with our regulators to make sure our plans are funded.
We're also investing nearly £4 billion in the 'Super Sewer', Thames Tideway Tunnel. The tunnel will capture all of the ‘first flush’ from the sewers after heavy rain.
How do I find historical data on storm discharge?
We publish annual reports back to 2019. If you need data from previous years, please email us to submit an Environmental Information Request.