A MAJOR programme of sewer upgrades is paying dividends in a Cornish village, where storm overflow spills have fallen by 30 per cent in just a year.

Engineers from South West Water have been working behind the scenes in the rural village of St Neot, near Liskeard to tackle a persistent problem – groundwater leaking into ageing sewer pipes during heavy rainfall.

The issue, known as infiltration, occurs when saturated soil builds up pressure and forces water through small cracks in pipe joints or manholes. Although this water does not come from homes or businesses, it still enters the wastewater network, increasing the volume the system must handle and raising the likelihood of storm overflows during wet weather.

Project manager Charlie Ford said addressing that hidden inflow was the first and most important step.

“At St Neot, a big part of the challenge was groundwater finding its way into the sewer network,” he said. “When that happens across multiple sections of pipe, it significantly increases flows during wet periods and puts added strain on the system.”

Instead of resorting to disruptive road closures and deep excavations, engineers opted for trenchless technology. Around 200 metres of sewer pipe were relined internally, effectively creating a new watertight pipe inside the old one.

Before the lining could be installed, crews used high-pressure water jets to thoroughly clean the pipes, removing debris and build-up. The lining process then sealed cracks and weak joints, preventing groundwater from seeping through.

Ford described it as “like building a new pipe within a pipe”.

“It strengthens the structure without the need for major excavation,” he explained. “Once sealed, groundwater can’t leak in through cracks caused by wear and tear, tree roots, or ground movement.”

Several manholes were also sealed to stop water penetrating through brickwork and mortar joints – another often-overlooked source of infiltration.

Alongside the structural repairs, operational improvements were introduced. A new control panel has altered the way pumps function at the site. Previously, the system experienced sharp peaks and troughs in flow during periods of intense rainfall. Now, the pumps operate more steadily, smoothing pressure changes and allowing the network to cope more effectively with sudden downpours.

The combined impact has been gradual but measurable. Storm overflow activity in 2025 dropped by nearly a third compared to 2024, marking a significant improvement for a small rural network.

The St Neot scheme forms part of South West Water’s wider £16-million Infiltration Reduction Programme, which targeted 175 high-risk sites following a review of performance across more than 1,600 storm overflows in the region.

And the work is not finished. A further 900 metres of sewer pipe in the village have now been surveyed as part of the next phase, helping engineers identify additional areas where targeted repairs could further reduce the need for storm overflows.

For residents, the benefits may be largely out of sight, but the improvements are clear. By strengthening ageing infrastructure and reducing unnecessary water entering the system, the upgrades are helping to protect both the local environment and the resilience of the wastewater network for years to come.