Huge swathes of the Greater Dublin Area were put under an unprecedented boil water notice last night, leading to panic buying and empty shelves in some stores.
The notice, a response to a breakdown in the disinfection process at the Leixlip Water Treatment Plant, affected in the region of 600,000 customers.
Five local authorities, including Dublin City Council, Fingal County Council, South Dublin County Council and Meath and Kildare county councils are impacted by the largest ever boil water notice issued by Irish Water.
The notice, issued at 5pm yesterday, went into effect immediately until further notice and applies to all homes and businesses operating in the affected areas.
Large sections of north Dublin city and county are affected, including Finglas, Glasnevin, Ashtown, Cabra, Poppintree, Darndale, Coolock, Artane, Killbarrack and Baldoyle.
In Tesco Blanchardstown, panicked customers quickly cleared the shelves of its water supply, leaving only sparkling bottles behind.
Swords and the surrounding area as well as the largely populated communities along the east coast from Balbriggan south to Sutton and Howth are affected, including Skerries, Rush, Lusk, Donabate, Malahide, Portmarnock, and Baldoyle.
Large commuter belts in Co Kildare - including Maynooth, Celbridge, Leixlip as well as parts of Co Meath from Stamullen to Garristown and the Naul are also affected.
"The Boil Water Notice has been issued with immediate effect for the entire supply as a precautionary measure following issues with the treatment process at the water treatment plant which may have compromised the disinfection process," Irish Water said.
"The issues have now been resolved, but water is travelling through the system which is why the boil water notice is being out in place."
Irish Water could not say when the notice would be lifted last night, but a statement said that it is working to resolve the issue as soon as possible.
In the meantime, the utility is contacting all vulnerable customers - such as the elderly - who are registered with them to advise them of the notice.
Updates and a map of the affected areas are available on the Irish Water website on www.water.ie. The customer care helpline is also open 24 hours a day with updates on 1850 278 278.
The notice advises all consumers to boil water for:
• Drinks made with water.
• Preparation of salads and similar foods which are not cooked prior to eating.
• Brushing of teeth.
• Making of ice - householders should discard ice cubes in fridges and freezers and filtered water in fridges. They are advised to make ice from cooled boiled water.
Unboiled water from taps and cisterns can still be used for bathing and flushing of toilets.
Meanwhile, customers trying to find out if their area has been impacted were left dismayed last night when the Irish Water website crashed.
A high volume of traffic led to a glitch that made the website temporarily unavailable.