615,000 people face a third day of boiling their water today in Dublin, Kildare and Meath.
Testing at the Leixlip treatment plant is continuing, after heavy weekend rain affected water quality and triggered a major boil water notice.
The boil water notice will not end until tomorrow at the very earliest.
Three test results proving acceptable quality levels must come back before the ban can be lifted.
The final sample is due later this evening, when a decision will then be taken by health authorities on the boil water notice.
The affected householders were impacted by a separate three day ban just two weeks ago.
Now Irish Water is warning of further boil water notices for people served by the Leixlip plant, until it is upgraded.That is due to be done next summer.