Dark Fibre

Key information:

The UK faces a significant water supply-demand problem – with a forecasted deficit of four billion litres a day by 20501, driven by climate change and population growth. To ensure that all customers have a reliable and sustainable water supply, the water industry has committed to reduce leakage by a third by 20302.

One way of protecting the increasingly precious supply of water is to reduce leakage from the network through better leak detection. This is a vast challenge given the 350,000km of water mains in England and Wales that need to be monitored.

Traditional leak detection tools analyse water flow and pressure data to highlight areas for investigation. In recent years, this has been enhanced using permanently-installed acoustic loggers- sensors that listen for leaks and raise concerns.

The introduction of acoustic loggers has improved how water companies detect leaks, but the scale of investment and speed of deployment is a significant challenge. Acoustic loggers need to be placed 100m-200m apart; and currently, leak alarms require human confirmation. The number of false alarms can be as high as 60%. This represents a vast investment, ongoing cost and logistical challenge to install and maintain these assets. To fulfil leak reduction targets and maintain water supplies into the future, the industry urgently needs a quick, easy, reliable, and cost-effective way to detect leaks.

The Dark Fibre project, funded by the Ofwat Innovation Fund, investigated the possibility of using existing optical fibre networks for leak detection.

The system uses a laser to detect noise along ’dark fibres’ (unused fibre optic cables) that can be deployed inside or alongside a water main. If new fibre was required to be installed for this method, it would be expensive and disruptive to introduce, but significant fibre networks already exist across the country for systems such as broadband and railway signalling. Much of this is already close to water industry assets.

The project undertook experiments which proved that the currently dormant ‘dark fibre’ could be used for water leakage detection, lowering the cost and environmental impact of the technique. It demonstrated that leak noise could be detected by a fibre up to 5m away and that the impact of leaks on ground stability could be detected up to 20m from the leak.

The project has now entered a second phase, Dark Fibre 2, which will look at scaling the technology and deploying it in a real-life scenario. It will also explore the extent to which the fibre and water pipe networks overlap to work out what portion of the English and Welsh water network can be monitored by the dark fibre solution.

This case study was featured in the Ofwat Innovation Fund 2023 annual report – read more: