Blockage Detection: StormHarvester & South West Water – Preventing Sewer Overflows Through Early Action
1. THE BACKGROUND
South West Water’s relationship with StormHarvester began in 2023, following an evaluation of smart and AI-driven solutions across the sector. Having heard about the significant benefits other water companies were achieving, and with StormHarvester carrying a strong reputation within the industry, South West Water were keen to explore what improvements could be made to their rate of detection.
They intended to do a six-month trial but StormHarvester proved so compelling that the decision to roll out fully was made just three months in. The results from the blockage detection trial showed the benefits were well beyond what South West Water’s existing monitoring could deliver, and the case for full deployment was clear.
2. THE SOLUTION
StormHarvester’s AI-powered platform continuously monitors South West Water’s sewer network using live level data, hyperlocal rainfall, and machine learning to detect abnormal patterns, including spikes, dips, flatlining, or erratic readings.
Identifying early warning signs of disruption allows you to:
- Receive precise, timely alerts
- Act quickly to prevent spills and flooding
- Reduce environmental harm and protect communities
3. THE DEPLOYMENT
South West Water started with a phased rollout approach informed by learnings from the trial itself, adding approximately 300 sites per month. During the initial onboarding, data accuracy was a challenge on South West Water’s side, such as ensuring spill heights were configured correctly which resulted in high volumes of false positive alerts until the data was refined.
The phased approach gave the team time to work through data issues in increments to ensure each batch of sites were performing accurately before the next was added, ensuring that they were not overwhelmed by false positives across all 1,400 Combined Sewer Overflows.
4. THE OUTCOME
The blockage detection trial delivered results that far exceeded what South West Water’s existing monitoring had been able to provide. The benefits were clear and significant, giving the confidence needed to commit to a full deployment across all circa 1,400 Combined Sewer Overflows. Scaling from the initial 300 trial sites by onboarding an additional 300 sites each month until complete coverage was achieved.
StormHarvester achieved a reactive alert noise reduction of 93%. Utilising our proactive alerts, 363 issues were successfully identified, while a further 395 proactive investigations were carried out.
5. EXAMPLE 1
- Levels above expected, alert sent to South West Water 10/10/25
- Work order raise the same day to investigate an unusual, elevated level
- Crew found a hard brush wrapped in rag
- Levels returned to normal after intervention
On arrival
Hardbrush wrapped in rag removed
6. EXAMPLE 2
- StormHarvester sent an alert 03/06/25 as levels were above expected
- Work order raised the same day, and crew attend within 4 hours
- Crew found large amounts of rubble in the line following a manhole lid replacement
- Levels returned to normal after clearing debris and washing down the line
Before
During
After
“StormHarvester’s data and customer service was responsive and accommodating. South West Water had regular calls with the StormHarvester team as they onboarded, resolving data issue trends quickly and effectively.
Aligning to our Smart Monitoring Strategy, we are constantly seeking continuous improvement, meaning looking at the services, solutions and innovations available and how this could ultimately improve our environmental performance.””
Adam Rousell, Proactive Control Manager, South West Water