South West Water has reduced storm overflow spills in St Neot, near Liskeard, by upgrading sewers to improve its local wastewater system.
Engineers at South West Water have been working on ways to stop groundwater leaking into pipes, a problem known as infiltration.
When soil becomes saturated after heavy rainfall, water pressure builds in the ground.
If there are small gaps in the joints on pipes or in manholes, groundwater can seep in.
That extra water isn’t coming from homes, but it still travels the same journey to the wastewater treatment works.
Charlie Ford, South West Water's Project Manager for St Neot, said stopping that unwanted water getting into the pipes was the first priority.
“At St Neot, a big part of the challenge was groundwater finding its way into the sewer network. When that happens across a number of pipes, it can increase the volume of water flowing through the system significantly during wet periods."
Rather than digging up roads, engineers used trenchless repair techniques. Around 200 metres of sewer pipe were lined internally, creating a watertight layer inside the existing pipe.
A number of manholes were also sealed to prevent water seeping through brickwork and joints.
Before lining, the pipes were cleaned using high-pressure water jets.
Charlie describes the relining process as like building a new pipe within a pipe:
“It’s a way of strengthening the pipe without major excavation and when they’re sealed, groundwater can’t leak in through those cracks or damage caused by trees, unwanted objects, or animals.”
The way pumps operate at the site has also been adjusted thanks to a new control panel.
Instead of sharp peaks and troughs in flow, the pumps now run more steadily, smoothing out pressure in the system and helping it perform more consistently during heavy rainfall.
The impact is gradual but measurable and saw storm overflows drop 30% in 2025 compared to 2024.
St Neot formed part of South West Water’s £16 million Infiltration Reduction Programme, which targeted 175 high-risk sites after reviewing performance across more than 1,600 storm overflows.
A further 900 metres of sewer pipe in St Neot have now been surveyed as part of the next phase of work, helping engineers identify where additional repairs may reduce the need for storm overflows even further.
Watch the video of South West Water's Head of Tactical Asset Management talking about the improvements in St Neot.