Water restrictions came into force in the Dublin region at 8pm tonight and are expected to continue for several days.
The move, a result of an as yet unidentified problem at a water treatment facility in Co Kildare, has been widely criticised.
Dublin City Council engineer Michael Phillips said many people will have no water between 8pm and 7am for the next five days.
Households and businesses in Fingal, South Dublin county, Dún Laoghaire Rathdown, Dublin city council areas, well as parts of Kildare and Wicklow, are to experience a restricted supply, he said.
Fianna Fáil councillor Mary Fitzpatrick said the water shortage issue highlighted the “absurdity and unfairness” of introducing water metering. “The Government is making a major mistake prioritising metering ahead of fixing leaks and building new water sources,” she said.
Minister for the Environment Phil Hogan “must be embarrassed to charge people for water services that are unreliable and subject to regular restrictions,” she said.
Minister for Public Expenditure Brendan Howlin said today that Irish Water would be established on January 1st “with a very significant capital budget to ensure there is adequate water supply.”
Mr Howlin said that for too long responsibility for water supply had been disparately spread out amongst local councils and that he hoped a national body would provide a “world class service.”
The restrictions will result in lower water pressure and the likely loss of supply. The restrictions are to assist the councils in replenishing supplies of treated drinking water to a normal level.
The serious water production problem arose at the Ballymore Eustace Water Treatment Plant in Co Kildare last weekend. The problem at the plant has caused a significant reduction in water production since.
Mr Phillips said the councils were hoping the restrictions could be lifted after Monday but he warned that disruption to supply “could go on longer”.
When asked how long the restrictions would last, he told RTÉ's Morning Ireland: "We have no idea...we will be reviewing it on a daily basis."
The characteristics of water had changed in terms of colour and turbidity (cloudiness), Mr Phillips said. However, he said he did not know what was causing the problem.
The plant was having difficulties getting out these particles using the current treatment process and was trying different ways to improve this, he said.
However there was "absolutely no danger" in the quality of the water product which he said met the standards required by the Environmental Protection Agency.
Mr Phillips urged householders to conserve water with minimum use of washing machines, dishwashers and power showers. He said the council sympathised with the problems this could cause for businesses in the hospitality sector but added that water supplies in Dublin operated on a “knife edge”.
Labour TD Kevin Humphreys criticised the introduction of restrictions.
“We cannot continue to have recurring water shortages in a city region that is trying to compete internationally for investment, visitors and trade,” Mr Humphreys said .
He said that, with 10,000 people visiting the capital for the Dublin Web Summit, it was “embarrassing that hotels and restaurants would have to ration water.
Mr Humphreys said a “new source of water” needed to be put in place to secure future growth and he supported the Bord Na Móna Garryhinch supply project to capture excess water on the Shannon. This project should be “fasttracked” by Irish Water when it begins its work, he said.
