600,000 people across large parts of Dublin are being told not to drink their tap water.
Treatment "issues" mean, without being boiled; drinking it, cooking with it or even using it to brush your teeth could cause stomach cramps and diarrhoea.
Irish Water and the HSE are meeting to decide if it's safe to lift the largest boil water notice the country's ever seen.
The order follows issues with the treatment process at a water treatment plant in Leixlip.
While the problem has been fixed, the system needs to be flushed out before tap water is drinkable again.
Large parts of Fingal, areas in Dublin City Council and parts of South Dublin County Council are affected.
People in parts of Kildare and Dunboyne in Meath are also being told it's not safe to drink their tap water.
A detailed map of affected areas is available here.
The warning has sparked panic buying with people stocking up on bottled water.
All registered vulnerable customers who are affected by the Boil Water Notice will be contacted with advice on what to do.
