Update: Scottish Water lifted restrictions on Friday afternoon on the remaining 20 properties in Whalsay that had been advised not to drink or cook with the water supply.
Those homes were in Vaivoe and Skaw areas of the island can now be used as normal.
Scottish Water said they would continue to flush the water mains out over the weekend. Aluminium levels had already reached an “acceptable” level, the organisation said.
“Our teams have worked hard to resolve this issue as quickly as possible and we want to thank those affected customers for their patience and understanding over the last few days,” according to a Socttish Water statement.
Whalsay residents have been advised not to use tap water for drinking or cooking after higher than normal levels of aluminium were discovered.
Scottish Water issued the advice with “immediate effect”. Customers in Marrister, Brough, Challister and Skaw are affected.
The move comes weeks after a new “state of the art” water treatment plant came online.
Some customers reported an unusual taste in the water. Scottish Water detected the spike in aluminium levels and in a statement said work was taking place to “resolve this problem and to return supplies to normal” Efforts were also being taken to ensure there were enough “resources” in Whalsay to help customers.
An information leaflet and bottled water are being delivered to all affected properties overnight.
A new water treatment works recently came on stream in Whalsay which Scottish water said was “producing very high-quality water”.
The £5 million plant at Huxter includes a “nano-filtration system and reverse osmosis technology”. Earlier this month senior project manager David Kitching said customers would “benefit from fresher, cleaner water from the state of the art” plant.
The supplier blamed “the existing older water network and pipes in the affected area [for] changing the characteristics of the newly supplied water, resulting in a deterioration of water quality and requiring the implementation of this restriction.”
The system is being flushed and a “robust programme” of sampling is taking place.
Scottish Water’s statement added: “Public health is our main priority at all times and we have robust procedures in place to monitor and analyse water quality. We would ask customers to follow the advice that has been issued, while we work to resolve the current problem. We want to apologise to customers for the inconvenience this issue has caused.”