# Portsmouth Water to use Openreach fibre to listen for leaks > Portsmouth Water is partnering with Lightsonic to use distributed acoustic sensing on Openreach's Full Fibre network. Lightsonic says the system can locate leaks to within 10 metres; rollout starts in December. Published 4 November 2026 by The Water Wire. Topic: Investment & infrastructure. Canonical: https://waterwire.co.uk/story/portsmouth-water-fibre-optic-leak-detection Portsmouth Water will introduce Lightsonic's Distributed Acoustic Sensing (DAS) technology across parts of its network ([Water Magazine](https://www.watermagazine.co.uk/2026/11/04/portsmouth-water-to-introduce-fibre-optic-leak-detection-technology/)). The system turns existing Openreach fibre-optic cables that run near water pipes into a continuous listening network. Portsmouth follows Affinity Water and Southern Water in using the service. ## What we know - **Detection:** the system reads changes in light signals along the fibre caused by vibrations from a leak. Lightsonic says it can locate potential leaks to within 10 metres. - **Infrastructure:** it uses Openreach's Full Fibre network rather than new sensors in the ground. - **Track record:** Lightsonic says technicians using the Openreach partnership have found up to four times more leaks than with traditional methods. It says the system saves more than one million litres a day for every 100km of network. - **Timing:** rollout begins in December 2026, ahead of winter, when cold weather increases bursts. Chief executive Bob Taylor said the technology would help the company "find more leaks across our network and carry out repairs sooner". ## What others are reporting [ISPreview](https://www.ispreview.co.uk/index.php/2026/10/portsmouth-water-adopt-openreachs-uk-fibre-broadband-network-to-detect-leaks.html) reported the deal on 23 October and adds the limits. The method works only where a leak is close to Openreach cables, and it currently runs on spare fibres rather than live broadband lines. Openreach plans to extend it to active fibre but has not yet done so. The outlet also notes that the service currently depends on Openreach, though alternative fibre networks could offer it in future. Openreach's Trevor Linney said there was "growing interest from water companies". ## Background The technology was first trialled with Affinity Water at five sites around London, covering 650km of pipes. In its first three months it located more than 100 leaks and was estimated to save about 2 million litres a day ([The Register](https://www.theregister.com/2026/03/13/openreach_fiber_water_leaks/)). The Register's caveat was blunt: detection saves water only if companies fix what it finds, and it described the wider sector's response as "positive noises" at the time. Southern Water followed in September, planning to trial the system over the winter. ISPreview reported that Affinity's savings had risen above 4 million litres a day across the 650km ([ISPreview](https://www.ispreview.co.uk/index.php/2026/09/southern-water-harness-openreachs-uk-fibre-broadband-network-to-detect-leaks.html)). The same report notes that about 60% of England's water mains are 45 years old and 13% are more than 100 years old. > **3,336km** — length of Portsmouth Water's distribution network ([source](https://www.gov.uk/government/publications/water-only-companies-in-england-environmental-performance-report-2025/portsmouth-water-environmental-performance-data-report-2025)) Portsmouth is a small company with a 3,336km network ([Environment Agency](https://www.gov.uk/government/publications/water-only-companies-in-england-environmental-performance-report-2025/portsmouth-water-environmental-performance-data-report-2025)). That makes its rollout a useful test of how much of a network can be covered from existing fibre. ## What we don't know yet - How many kilometres of Portsmouth's network will be covered, and what it will cost. - Whether results will be published independently of Lightsonic's own figures. - When live, rather than spare, fibres will be usable. ## What to watch - First results from Portsmouth and Southern Water over the winter. - Whether Affinity moves from pilot to full contract. - Ofwat's leakage reporting for 2026-27, to see whether detection gains turn into lower reported leakage. Reusing telecoms fibre avoids much of the capital cost and disruption of installing sensors across a whole network. That makes it attractive to a small company, and to larger ones facing leakage penalties. The early evidence comes mainly from the vendors, Lightsonic and Openreach, and from one pilot. Portsmouth's rollout should show whether the results hold up on a different network. The constraints are real. Coverage depends on where Openreach's spare fibre runs, so the technology complements other methods rather than replacing them. Finding more leaks also creates more repair work, so the benefit depends on a company's capacity to fix leaks quickly. The Register's point stands: detection is only half the job. The other strategic issue is dependence on a single network operator. Water companies may want to see competing fibre networks offer the same service before building it into long-term leakage strategies. ## Sources - [Water Magazine — Portsmouth Water to introduce fibre-optic leak detection](https://www.watermagazine.co.uk/2026/11/04/portsmouth-water-to-introduce-fibre-optic-leak-detection-technology/) - [ISPreview — Portsmouth Water adopt Openreach's UK fibre broadband network to detect leaks (23 October 2026)](https://www.ispreview.co.uk/index.php/2026/10/portsmouth-water-adopt-openreachs-uk-fibre-broadband-network-to-detect-leaks.html) - [ISPreview — Southern Water harness Openreach's UK fibre broadband network to detect leaks (23 September 2026)](https://www.ispreview.co.uk/index.php/2026/09/southern-water-harness-openreachs-uk-fibre-broadband-network-to-detect-leaks.html) - [The Register — Openreach: Fiber can sniff out leaky water pipes (13 March 2026)](https://www.theregister.com/2026/03/13/openreach_fiber_water_leaks/) - [Environment Agency — Portsmouth Water environmental performance data report 2025](https://www.gov.uk/government/publications/water-only-companies-in-england-environmental-performance-report-2025/portsmouth-water-environmental-performance-data-report-2025)