Storm overflow performance

Storm Overflows and Event Duration Monitoring

We measure the frequency and duration of storm overflow operations using Event Duration Monitors (EDMs) and have reported on this since 2020.

There are over 2,200 storm overflows in the North West, and all are now monitored.

We have a greater understanding of the region’s vast 78,000 km wastewater system than at any point in history, analysing over 500 million rows of data to highlight any area requiring further action.

2022 Performance Data

In 2020, we reported data from 1,932 monitors. 

In 2021, we reported data from 1,994 monitors. 

In 2022, we reported data from 2,004 monitors. 

Since 2020, this shows:

  • 39% reduction in spill numbers
  • 41% reduction in spill duration
  • 41% reduction in the average annual spill frequency

We have achieved this by:

  • investing to reduce how often overflows operate - between 2020 and 2025 at least £230m will have been invested to improve 184km of rivers; and
  • steadily improving the quality of the data we report

Whilst 2022 was an average year for rainfall in the North West, the EDM data may well go up and down in the years ahead depending on the weather. We do, however, expect to continue to see an overall downward trend in the number and duration of storm overflow operations as we deliver our largest ever environmental programme to re-plumb the North West’s drainage network

Our performance in 2022 means we have already met our target to reduce the number of storm overflow operations compared to the 2020 baseline. This is one of the commitments in our Better Rivers: Better North West plan.

You can download our data returns below:

2020 EDM data 

2021 EDM data - original

2021 EDM Data - Version 2*

2021 EDM data - Version 3*

*As our data accuracy improves we have provided updated information as appropriate.

2022 EDM data