Event duration monitoring

Our EDM annual report

We share our EDM data with the Environment Agency annually and the 2024 returns are also published here to ensure customers have all the information they need about storm overflows.  

For 2024, we are publishing our Environment Act Storm Overflow Report which includes our annual EDM return data. To go beyond this, we have also included some additional data about whether the asset is a discharge that is permitted by the EA, the grid reference of the discharge and the waterbody that it discharges into. We have also included details of the investigations and improvement schemes we have undertaken as part of the Water Industry National Environment Programme (WINEP).  

You can also have a read through the reports we’ve published in previous years.

How is the data pulled together and validated?

We’ve collected over 150 million data points during 2023 and spent time validating the data to make sure it is as accurate as possible. We do have some data quality issues which we are investigating such as where data is missing, negative or flatlining.

We have investigated over 650 overflows which discharge the most to understand if the data is representative of performance, with resolution activity and further investigations ongoing.

If there’s been an issue with the monitor, such as a failure or an environmental factor that’s caused a false reading, we’ve flagged the data and manually corrected it. We have a full audit trail for all corrected data.

What we’re doing to improve

We are seeing a combination of factors, from urbanisation to climate change, frequently testing the design and capacity of our network. At the same time, increased awareness of the operation of storm overflows is driving an important debate on what society sees as acceptable. We’re committed to going above and beyond the DEFRA Storm Overflow Taskforce activity in ending pollution from storm overflows.

In Yorkshire, we have 2,190 overflows and we know replumbing the whole of Yorkshire is an enormous task that would be both disruptive and costly to customers, and we need to ensure water bills remain affordable, but we are committed to playing our part to improve Yorkshire’s rivers and coastline.

To help drive improvements, with support from our shareholders, we’ve started a £180million investment programme to reduce discharges from the overflows we know are operating more frequently.

Storm overflows are a priority for us and the programme will be looking at four ways of reducing overflows - creating storage in the system for the stormwater, separating surface water out, stopping infiltration, or making changes to other assets like our pumping stations so we’re passing forward the right flows.

Separating surface water out could include creating SUDs, so we’re slowing the flow of water. We’re also looking at water butts so we can disconnect drainpipes from roofs and store the water for watering gardens instead of it going into our sewer system.

All of the work we’re undertaking will take us beyond the government’s storm overflow reduction plan and we’re already planning our largest ever environmental investment programme between 2025 and 2030.