Water supply is being restored to Dublin city after a high pressure main burst yesterday, affecting thousands of homes and businesses.
Uisce Éireann said repairs to the water main have been completed as crews worked through the night to restore supply.
A number of schools in Dublin city are closed as a result of the burst main.
A Department of Education spokesperson said the decision to close a school rests with the school management authority, taking into consideration the full guidance and direction available from the principal response agencies.
Meanwhile, Uisce Éireann said it will take several hours for normal supply to return to all customers, especially for those on higher ground.
The company also said there will be a lot of airlocks and discolouration in areas across the city.
Speaking on RTÉ's Morning Ireland, the Head of Water Operations at Uisce Éireann said supply has been restored for many customers.
Margaret Attridge said that some customers will still be waiting for supply or normal pressure to return as "it's going to take time", particularly for those at the "extremities" of the network.
She warned that with any outage like this there can be water discolouration.
"We are asking people to run their taps for a period to clear this discolouration and if it persists to log the issue with our call centre so we can get network crews out."
Ms Attridge said the water is "safe to drink but very unsightly."
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Uisce Éireann was alerted at 10am yesterday that a significant and high pressure water main had burst in Dublin's south inner city.
The road on Marrowbone Lane partially collapsed following the incident.
Water supply to the pipe was switched off in an effort to establish the cause of the problem.
As a result, 40,000 premises across the capital were left with low pressure or no water at all.
Ms Attridge said it was "a difficult and deep dig" to fix the main.
"It was a pipe that was laid about 40 years ago but since then other utilities come along like gas, ESB, Telecom cables have been laid across it ... and poor ground conditions beside old buildings."
She said Dublin city crews got to the pipe around 6pm and managed to repair it around midnight with pressure being restored from around 2am.
"It was a high pressured main as it supplies homes and businesses from Dolphins Barn ... across the city out through Clontarf and Raheny."
Ms Attridge said while there are 42,000 homes in that area of Dublin, the network crews managed to keep supply to many customers during yesterday.
She said the fear was that the pipe would be fractured but they found out it was actually the fitting on the top of the pipe that "sheared off".
She said with a pipe that size it might happen once a year and have an impact on an area of that size.
"This pipe would not burst frequently. It would not be top of our list for replacement. A pipe of this size would not be prone to failure. It wasn't the pipe that failed. It was the fitting on to it that failed."