A boil water notice has been re-issued for customers supplied by the Leixlip Water Treatment Plant.
It affects 600,000 people across Dublin, Kildare and Meath.
Irish Water says the notice is in place as a precaution.
In consultation with the HSE, as a precaution, a Boil Water Notice to protect the health of customers supplied by Leixlip Water Treatment Plant has been put in place for a second time. More details to follow shortly.
— Irish Water (@IrishWater) November 4, 2019
It's come following long spells of heavy rain.
Irish Water says turbidity in the source water for the old Leixlip Plant has exceeded acceptable levels.
Eamon Gallen, Irish Water’s General Manager said: "We are very disappointed that a Boil Water Notice has to be imposed again but as we outlined the last time, our number one priority is the public health and the safety and well-being of our customers."
The utility is due to appear before an Oireachtas Committee tomorrow to answer questions about the previous notice:
Boil water notice resumed for North Dublin. We will have Irish Water in before @OireachtasNews Committee at my suggestion tomorrow at 1 where I will work to get answers on this important issue. pic.twitter.com/zcOl3vSFuz
— Noel Rock (@NoelRock) November 4, 2019
