Restrictions to Dublin's water supply at night time could last weeks.
Following leakages caused during Storm Emma, Irish Water is battling to meet growing demand.
Water pressure to 1.2 million buildings across Dublin city and country will be reduced from 8pm-6am to try and deal with the shortage.
The organisation has admitted that restrictions could have to continue for "a number of weeks".
Irish Water says the decision to reduce pressure across the Dublin network "was one that was not taken lightly", and admitted it is "assessing the impact of the 12 hour reduction".
"We are leveraging the best expertise across Irish Water and the 4 Dublin Councils to move water around the network and protect supply", a statement said.
"We are aware that some people were without water entirely and we will review with water engineers across the Dublin Councils today to see how we can minimise this impact."
Hospitals are having water diverted to them, while three huge leaks in the North Docklands, Infirmary Road and Skerries have now been repaired.
Irish Water says they were wasting the equivalent of the daily water usage of Balbriggan which has a population of about 25,000,
Irish Water managing director Eamon Gallen says there are still “severe concerns about the greater Dublin area” with reservoir levels extremely low.
He said the area “saw an increase of 10% in demand from Friday to Sunday.”
“At the moment, despite having our plants working at peak output, storage is significantly depleted,” he said.
Reservoir storage in the Dublin area dropped by over 30 million litres over the weekend.
There was a surge in demand of 60 million litres a day nationally during the cold snap with a 20% rise as the thaw took hold.
The depleted reservoir levels around the country are partly due to households and businesses that decided to leave taps running to prevent pipes from freezing.
Irish Water is warning not to leave anything running during periods of cold weather and Mr Gallen noted that “it affects everybody if you leave it run.”
He said running taps “draws down all the water obviously straight away” adding that it also makes it difficult to tell where there are leaks in the system.
“I think it is something we were thought as we grew up; ‘leave a tap running and it won’t freeze,’” he said.
“Things have moved on and pipes are generally that much deeper under-ground; once they are under two feet you are generally fine.”
He said people need to “understand that this is not the thing to do.”