Chemists from the UK are being sought to try to solve the water treatment issue leaving much of greater Dublin without proper supplies.
The city is 30 million litres below what it needs to keep taps and toilets in homes and businesses flowing after a 10-day old problem at the Ballymore Eustace plant in Co Kildare.
Production was cut by about a fifth, prompting damning criticism from restaurateurs who claimed Ireland was a third world country hit by water shortages in summer and winter regardless of the weather.
Severe restrictions will hit supplies in Dublin city and county and into Kildare and Wicklow.
Many people will have no water between 8pm and 7am each night until Monday at the earliest.
Dublin City Council engineers held talks with the Environmental Protection Agency over the treatment crisis after a change in the make-up of raw water coming into Ballymore Eustace from the nearby Poulaphouca reservoir.
The council has its own engineers and lab specialists on site in Kildare and is also seeking advice from consultants in the UK with expertise in the area.
The supplies are a different colour and turbidity or cloudiness than the system is used to handling.
It is suspected the fine, dry summer followed by periods of heavy rain over the last few weeks has created an unusual balance in the raw water.
Pollution is not an issue and the quality of water making it to taps is not a concern.
"Consumer behaviour can help us enormously. If you don't waste water, run taps, it will go a long way to putting capacity into the system," a Dublin City Council spokesman said.
People living and working in areas of higher elevation will be worst affected by shortages but the council has no plans to send water tankers to housing estates.
It said it will review levels in the treatment plant and reservoirs tomorrow at 11.30am.
Fire chiefs also expressed concern that tenders will not be able to tap mains to replenish their tanks over the busy Halloween nights.
"Clearly it will be a drain on existing resources because additional fire engines (which carry a five minute water reserve in their tanks) will have to attend at the scene because of the lack of access to mains water and the limited access to rivers, canals and lakes from which to fill engine tanks," John Kidd, Irish Fire and Emergency Services Association chairman, said.
Dublin operates on a 1% surplus of treated water supplies unlike most other European cities which are at about 15%.
At Easter supplies were hit because of an algae bloom.
"We had a water shortage during the summer, we have a water shortage now, and probably if we have snow in the winter time, we will have a water shortage again," he said.
Water treatment experts are trying to identify the right chemical, known as polyelectrolytes, or the right balance or dose of chemicals, used to force small particles in raw water to stick together allowing them to be filtered or cleaned out.
Mr Phillips has suggested the increased cloudiness of raw water may have been caused by the "fine summer" while the EPA suggested recent heavy rainfall may have played a part.
"It's mainly the change of the character of the water coming into the plant and it's proving very difficult to treat it," he said.
"There's no issue with the final water quality coming out - people do not have to worry about that, but production is down about 20%."
Mr Phillips added: "We don't know what caused the change in this."
Homes and businesses have been affected in Fingal, Dun Laoghaire-Rathdown, Dublin city and the south county areas, as well as into Kildare and Wicklow.
The Irish Hotels Federation (IHF) said that major hotels should not be affected by the restrictions as they have large tanks with enough water supplying enough for two days. It said once restrictions are lifted during the day tanks will be replenished.
Households have been urged to conserve water during the day as much as possible.
Tips include keeping a jug of water in the fridge instead of running the tap, only using the dishwasher and washing machine when full, turning off taps while brushing teeth, minimising toilet flushes and taking quick showers.
"Ten minutes in a power-shower uses 250 litres of water, two-and-a-half times more than a bath does (100 litres)," council chiefs said.
The water issue has also sparked criticism of the Government's plans to bring in water metering and charges.