St Neot storm overflow reduction has been achieved following sewer upgrades carried out by South West Water to improve the resilience of the village’s wastewater network. The project focused on reducing groundwater infiltration into pipes, a key contributor to storm overflow activations during periods of heavy rainfall.
Engineers addressed infiltration — the process where groundwater enters sewer systems through cracks, damaged joints or porous manholes — which can significantly increase flows to wastewater treatment works even though the additional water does not originate from homes.
St Neot storm overflow reduction through infiltration control
When soil becomes saturated after prolonged rainfall, pressure builds in the ground. If pipe joints or manholes contain small gaps, groundwater can seep into the sewer network. Across multiple assets, this can substantially increase system volumes during wet weather events.
Rather than undertaking large-scale excavation, South West Water used trenchless repair techniques. Approximately 200 metres of sewer pipe were internally lined, creating a watertight barrier within the existing structure. Manholes were also sealed to prevent groundwater entering through brickwork and joints.
Prior to relining, pipes were cleaned using high-pressure water jetting. The lining process effectively forms a new pipe within the original asset, strengthening structural integrity while preventing infiltration.
Charlie Ford, Project Manager at South West Water, said: “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.
“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.”
Operational improvements support wastewater resilience
In addition to physical repairs, pump operations were optimised through the installation of a new control panel. Instead of sharp peaks and troughs in flow, pumps now operate more steadily, helping smooth system pressures and improve performance during heavy rainfall.
The St Neot storm overflow reduction project has delivered measurable results. Storm overflow activations in 2025 fell by 30% compared with 2024 levels.
The scheme forms part of South West Water’s £16 million Infiltration Reduction Programme, targeting 175 high-risk sites following a review of performance across more than 1,600 storm overflows.
A further 900 metres of sewer in St Neot have since been surveyed as part of the next phase, enabling engineers to identify additional repairs that could further reduce reliance on storm overflows.
Read more about sewage management and storm overflow solutions.
