Dublin's four local authorities have urged people to conserve water due to a "serious production problem" at the Ballymore Eustace treatment plant.
The local authorities said nightly restrictions will be in place from tomorrow until at least next Monday.
The restrictions will last from 8pm until 7am and will be reviewed on a daily basis.
The authorities said they had reduced pressure at the plant after problem was discovered over the weekend.
However, it was not enough to restore drinking water levels to normal.
They said it could take some time to "resolve the issue", but stressed that there was no threat to the quality of the water.
The restrictions will result in lower pressures and loss of supply across the capital and surrounding areas.