At least 1,000 properties were left without drinking water on the Rosneath Peninsula on Thursday.
Since Thursday morning, people in the G84 Rosneath, Kilcreggan and Clynder areas were reporting no water, loss of pressure or intermittent supply of drinking water.
Scottish Water confirmed shortly before 10.30pm that supplies had been restored due to alterations made to the network.
It added that, despite investigations carrying on throughout the day, no fault has so far been located on the public network.
The firm said that additional staff and resources are “step-testing” the supply, which involves testing pressure at various points along the water main.
This is expected to continue through Thursday night and into Friday morning as long as conditions remain safe for operatives to work.
Six tankers of water, which were called in order to bolster water flow to customers, are no longer required – however, they will remain on site as a precautionary measure.
Once supplies restore, some people may experience discoloured water – the firm advises to run the cold-water kitchen tap at a reduced pressure until the water runs clear.
A spokesperson for Scottish Water said: “We are confident that we have restored drinking water to all customers in the affected area, and we have had no customer contact regarding loss of supply since early evening.
“Our operatives are working round-the-clock to locate the fault and we will let customers know if any further work may impact their supply once repairs get under way.
“Our thanks once again for the patience and understanding shown during this incident, and we sincerely apologise for the disruption.”