Storm Overflows Cut by 93% at Cornish Site Once Among Region’s Worst

One of Cornwall’s worst spilling storm overflow sites sees huge drop following £300k investment

South West Water has slashed storm overflow spills at Rilla Mill by 93%, reducing incidents from 293 in 2023 to 19 in 2024. The site, which was previously one of the top 10 highest spilling locations in Cornwall, has undergone significant upgrades as part of the water company’s wider drive to improve the region’s sewer systems.

What’s Changed at Rilla Mill?

The improvements come after a targeted investment of nearly £300,000. As part of the upgrade, South West Water has installed a new rapid balance tank to store excess flows during periods of heavy rainfall, and added a new inlet screen to enhance treatment capability.

The work forms part of the company’s wider Turning the Tide programme, a storm overflow investment plan aiming to deliver long-term environmental benefits across the region. The company says it is spending around £760 million to tackle the issue over the next five years, as part of a wider £3.2 billion investment programme.

Susan Davy, CEO of South West Water, said:
“Reducing the use of storm overflows is just as important to us as it is to our customers. Delivering change on this scale takes time, ambition, and record levels of investment. We have a 15 year programme to deliver the change we all want to see. My brilliant teams are out every single day, working harder than ever and Rilla Mill is another example of how teams are reconfiguring our system. It’s great to see their dedication and how much they care about making a real, lasting difference in the region we all live and work in.”

📷CEO Susan Davy and Wastewater Director David Swiggs

Tackling the Root of the Problem

Site Manager Karl Stone said his team has focused on addressing the cause of excessive flows, which was infiltration caused by increasing rainfall.
“My team and I have helped tackle the root causes of excessive flows which was infiltration due to more heavy rainfall than ever entering the system. We have worked almost 700 hours to line 584m of sewer and sealed 11 manholes – preventing the system from becoming overwhelmed and future proofing against climate change.

“We continue to monitor this site and have more planned as part of our commitment to meeting the Government’s storm overflow targets a decade ahead of schedule.”

Rilla Mill was South West Water’s fifth highest spilling site in 2023. The work carried out there is part of the company’s broader WaterFit programme, which is focused on reducing storm overflows, improving water quality, and supporting nature recovery.

You can track ongoing progress across the region through the WaterFit Live map.

📷Rilla Mill

📷Rilla Mill