The site is Guernsey’s largest treated water service reservoir, able to store 13 million litres of water – about the same as five Olympic swimming pools.
It was completed in 1965, supplying water to about 10,000 people, but it has been needing attention.
Work on the tank had been planned to take place, but was brought forward after routine water quality testing showed a single failure in November 2024.
The tank was immediately isolated from the supply to determine the cause, which, after draining the tank, turned out to be water ingress via the old roof membrane.
It was decided then that 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 Guernsey Water moved quickly, although undertaking this work in 2025 was not part of the plan. It reordered its maintenance 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,’ he said.
‘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.’
During the near year-long project, the tank, which is 55 metres long, 55 metres wide and 5.5 metres high, was drained so the inside could be cleaned and inspected.
Targeted concrete patch repairs were undertaken on the inside.
Outside, the ageing green roof membrane was removed and concrete joints were replaced. A stronger, multi-layered replacement waterproof roof covering was then applied.
Wire mesh baskets filled with stone – known as gabions – surround the roof, with some 1,100 tonnes of gravel in the middle, 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. It is now back in operation.
‘This vital piece of infrastructure has served the island for 60 years and provided billions of litres of water in the process,’ said Mr Falla.
‘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.’
This project was part of a larger £6m. capital programme of investment planned to take place this year alone, which included 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,' Mr Falla added.
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