Scottish Water is planning a series of works in Whalsay which, the organisation says, should result in major improvements to supply and treatment.
The works are due to begin this month, with more than £5.4 million being invested in the construction of a brand new water treatment plant to supply around 1,000 people.
The plant will replace the existing water treatment plant on the island.
The project also includes the building of a new pumping station next to the existing one on the banks of Loch Huxter and construction of a new 700 metre water main through rural land to the new plant.
Planning permission for all work has been granted by the council. The essential work will take around 10 months in total. Scottish Water contractor Ross-shire Engineering will be carrying out the work.
Scottish Water says the works should not result in any disruption to supply.
David Kitching, Senior Project Manager with Scottish Water, said: “This modern treatment works is the best in class and comes after an exhaustive design and planning process.
“It will give new levels of quality and resilience of supply for the people it serves and will secure the quality of water supply in the area for the next 20 or 30 years at least.”