£1.1 million critical infrastructure upgrade completed

Guernsey Water’s largest treated water service reservoir at Forest Road is now back in full operation following the upgrade – the most extensive in its 60-year history. The investment future proofs this critical asset to ensure it can continue to deliver clean, safe and wholesome drinking water to around 10,000 customers.
In a near year-long project, the tank was drained of its 13-million litres to allow specialist contractors to clean and inspect the entire internal structure. Targeted concrete patch repairs were undertaken on the inside of the tank.

Externally, the aging green membrane which covered the roof was meticulously removed by local contractor Geomarine, who also hand-filled the concrete joints that needed replacing. A stronger, multi-layered replacement waterproof covering was then applied to the roof. Wire mesh baskets filled with stone – known as gabions – surround the roof, with some 1100 tonnes of gravel in the middle, all to aid water runoff and provide additional UV protection for the new roof covering. Owing to roof weight limits, the gravel had to be placed with powered wheelbarrows.

New rainwater drainage has been installed including a new collection pond.

This was carefully assessed before the work started and designed to ensure an overall increase in biodiversity because of the project.

Capital Delivery Manager Carl Falla said:“This vital piece of infrastructure has served the island for 60 years and provided billions of litres of water in the process. Thanks to targeted network alterations, customers won’t have noticed any change during this upgrade process. This seven figure investment will future proof the site and ensure it continues delivering for Guernsey. Not investing simply wasn’t an option if we want a reliable, high quality water supply.”

“This project was part of a larger £6 million capital programme of investment to have taken place this year alone – including our new ring main project and manhole cover replacement project, to name just two. All these investments will make our network sufficient and resilient for decades to come.”

Work on the tank had been planned to take place over the coming years, but was brought forward after routine water quality testing showed a single failure in November 2024. The tank was immediately isolated from supply while we determined the cause, which, after draining the tank, turned out to be water ingress via the old roof membrane. It was decided the best and most comprehensive approach was the complete roof membrane replacement. No other failures were detected anywhere on the network.

Capital Delivery Manager Carl Falla said:

“Although undertaking this work in 2025 wasn’t part of the plan, we moved swiftly to reorder the programme and ensured the tank was returned to service as quickly and safely as possible. This shows the importance of ongoing investment in the renewal of our water networks and that drinking water quality is our top priority.

“This is why we test and this is why we invest: to ensure sufficient, resilient infrastructure is in place to provide clean and safe drinking water.”

The tank is 55 metres long, 55 metres wide and 5.5 metres high. It was completed in 1965.

No works were undertaken on the East Tank or Tower at this time. Future investments will be made. The Tower is in place to ensure water pressure in that area of the island is sufficient.