SOUTH West Water reduced storm overflow spills by 97 per cent last year at one of its highest spilling sites in Cornwall.

Carnon Downs Wastewater Treatment Works, between Truro and Falmouth, activated 290 times in 2023 and was one of the region’s largest spilling overflows.

Thanks to targeted improvements by South West Water, these spills were reduced to just eight in 2024 - the wettest hydrological year on record - and just one spill in 2025 so far.

Groundwater - the water found underground in the cracks and spaces in soil, sand, and rock - was found to be entering the sewers which flow into the works, and overwhelming it during periods of wet weather.

To hold these additional flows and prevent them from being released through the storm overflow, a new storm tank was built, providing up to half a million litres of extra storage.

The project also included a new pumping system and monitoring equipment to manage storm overflows effectively and ensure stored water is delivered to the treatment process as soon as there is capacity to treat it; a screening unit to remove debris before water enters the tank; and a manual washdown system to keep the tank clean and working at full capacity.

Andy Pettifer, South West Water’s wastewater operations manager for West Cornwall, said: “Our teams live and work in these areas, so we’re personally invested in getting it right. We have worked hard to make these changes, and it is great to see real improvements taking shape.”

South West Water is investing around £760-million over the next five years to reduce storm overflow spills across the region. It aims to become the first water company to meet the government’s target of achieving less than 10 spills per overflow, per year, a decade early by 2040.