A £3 million refurbishment of St Saviour's Water Treatment Works is underway.
Guernsey Water says the project will run in phases over the next couple of years.
It will involve switching from the current membrane filtration process to a rapid gravity filtration treatment one.
Guernsey Water says the current system has is nearing the end of its life, and it has been reviewing the latest water treatment technology for the most cost-effective and environmentally friendly options.
The rapid gravity filtration water treatment process and ultraviolet (UV) disinfection system is similar to that which was installed at the Juas Treatment Works.
Carl Falla, Capital Delivery Manager, says customers won't see any interruption in supply while the work is being done:
“Our phased approach to the refurbishment will mean that while parts of the site are worked on, others can still be online to meet our customers demand for quality drinking water. Our primary aim is to achieve a balance between maintaining output and allowing the complex improvement works to progress efficiently.
We want to reassure Islanders that while this is a major technical project for Guernsey Water, the quality or availability of water supplies will not be affected whilst works are carried out."

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