Uisce Éireann has completed works repairing a number of leaks on its supply line from Ballymore Eustace in Co Kildare to Saggart in Co Dublin.
The line carries over 200 million litres of water every day, one-third of all the supply to the Greater Dublin area.
The utility company says that the works, which involved more than 300 people, began on Friday night and were carried out in a 27-hour window.
When the water was switched off, the workers entered the pipe and walked up to 300 metres to reach the repair locations.
Following the work in which 15 leaks were repaired, Uisce Éireann said that treated water was now flowing through the pipeline and the water network was now returning to normal operation.
Nicola Butler, Programme Manager with Uisce Éireann, said that the repair works were carried out following months of planning and coordination.
“Our priority throughout the weekend was to carry out these essential repairs safely while keeping disruption to customers to a minimum,” she said.
“We would like to thank everyone for their support throughout this operation and for their continued efforts to conserve water, particularly local communities and landowners whose cooperation helped make these works possible.”