South West Water’s real-time monitoring network is driving faster action on storm overflows

Thanks to sustained investment, 100% of South West Water’s 1,342 storm overflows are now fitted with Event Duration Monitors (EDMs) which record data at least every 15 minutes, with some sites capturing updates every two minutes and others as often as every 10 seconds.

This high-frequency monitoring provides South West Water teams with a detailed, real-time view of the network. It allows them to detect rising flows, blockages or debris early and take faster, smarter action to prevent environmental impacts across the region.

Despite record-breaking rainfall in 2024, the wettest hydrological year on record, South West Water was one of only five companies in the industry to reduce spills compared to 2023 - with real-time monitoring playing a key role in this.

South West Water has reduced spills at beaches in the bathing season by 20% in the last five years and are continuing to take action on customers care about. The company has also removed ¾ of the top 20 spilling sites from 2023.

South West Water’s EDM’s operate reliably at 93.8%, the second best in the industry. EDMs are required to record data every 15 minutes - but many of South West Water’s monitors record data every two minutes, giving a much clearer, more responsive view of overflow activity.

This more frequent monitoring means South West Water can detect shorter, faster-moving events and respond in real time, while also making smarter long-term investment decisions based on richer, more reliable data.

How data can drive investment

A prime example of real-time data driving real change is at Duloe, one of South West Water’s highest-resolution monitoring sites.

In 2023, Duloe near Liskeard in Cornwall was among the highest spilling storm overflows in England. Limited storage and treatment capacity meant the site regularly struggled to manage incoming flows during heavy rainfall.

Here, EDMs record data every 10 seconds, well beyond the industry standard of 15 minutes. This high-frequency monitoring provided a much more detailed picture of activity on the network - revealing short, frequent spills that would likely have gone undetected with standard monitoring.

With this insight, South West Water was able to pinpoint the problem and invest directly at the source - installing a new 30,000-litre balance tank and adding a cloth filter to the existing storm weir at the local treatment works.

As a result, Duloe has seen a reduction in spills, with wider monitoring showing a significant improvement in overall performance. It’s a clear demonstration that high-frequency data doesn’t just show more — it enables smarter, faster investment where it matters most.

An investment programme powered by data

The insight provided by South West Water’s real-time monitoring network is the foundation of its £760 million storm overflow investment programme - the largest in the company’s history.

Over the next five years, this data-driven programme will deliver:

• Upgrades at high-priority sites – targeting overflows that spill most often or affect sensitive areas like bathing waters and habitats. Investments include increased sewer capacity, upgraded pumping systems, and intelligent flow controls.
• Expand storage across the network – building new storm tanks and detention basins to hold back excess water during heavy rain, reducing pressure on the system.
• Nature-based solutions – South West Water will work with the landscape to slow surface water before it enters sewers, through sustainable drainage, wetlands and catchment management.
• Smarter, more automated operations - using live data, sensors and predictive tools to manage flows dynamically in response to weather and network conditions.

Every part of South West Water’s investment programme is underpinned by real-time data, ensuring the investment goes where it will have the greatest impact.

CEO Susan Davy said: “Real-time data is transforming how we care for our environment. By seeing what’s happening in our network every few seconds, we can act faster, plan smarter, and invest where it matters most. Even in the face of record rainfall, this technology has helped us reduce spills and protect bathing waters — and it’s only the beginning. Our £760 million investment programme, driven by this data, will help us deliver cleaner rivers and seas for the South West, a decade ahead of national targets.”

This technology is a key part of South West Water’s plan to meet the Government’s storm overflow targets a decade early, delivering cleaner rivers, healthier seas, and a better future for the South West.