Irish Water says a boil water notice for customers supplied by Leixlip water treatment plant has been lifted.
An Environmental Protection Agency (EPA) audit of the old Leixlip plant, and satisfactory results of a number of water samples, led to the decision to lift the notice.
The EPA conducted their audit of the Leixlip plant on November 8th.
Irish Water, Fingal County Council were on site to support the audit and the Health Service Executive (HSE) were also present.
The EPA are expected to publish their findings next week.
Irish Water, the HSE, EPA and Fingal County Council say they will continue to liaise on the Leixlip water treatment plant, with "the protection of public health" being the number on priority.
Niall Gleeson is managing director of Irish Water.
He said: "Irish Water acknowledge and understand the impact of this boil water notice on the 600,000 people affected and we sincerely regret the inconvenience."
"We endeavoured to keep the public up to date at every stage and we are grateful to the media, elected representatives and members of the public who shared the information on social media and who supported family, friends and neighbours."
"We are grateful to our partners in Fingal County Council who worked with us to provide all of the necessary information to the HSE and EPA to facilitate the lifting of this boil water notice."
But he added: "The old plant at Leixlip remains vulnerable and Irish Water working with Fingal County Council will be working to minimise the risk of another boil water notice.
"We have maximised the processes to build resilience while also diverting water from Ballymore Eustace, the country's biggest water treatment plant, to decrease pressure on the old plant at Leixlip."
Irish Water said the notice was issued because previous rains led to “very cloudy” water entering the Leixlip facility.
It said it has two treatment plants at the facility and while the newer one was able to safely manage the influx of cloudy water, the old one was not.
The old plant supplies 20% of the overall daily water demand for the Greater Dublin Area.
