Some homes and businesses have been left with dirty water in the wake of a treatment crisis in supplies for Greater Dublin.
Despite assurances yesterday that quality was not an issue, the City Council has warned people who are getting brown, orange or yellow discolouration in supplies.
Engineers said some water was affected because of the disruptions in supply following problems at one of the state's biggest treatment plants, Ballymore Eustace, Co Kildare.
It warned anyone seeing a brown, orange or yellow tinge that it should not be used for drinking or cooking.
In its latest update on the crisis Dublin City Council urged householders experiencing the problem to run taps clear for two to three minutes.
"If the problem persists contact us for further advice. Typically the problem resolves within an hour or two of the water supply returning," the council said.
It also warned that it could take two to three hours from when valves on the pipes were opened this morning at 7am for full supplies to filter to every home and business in Greater Dublin.
"This is down to the location of the property relative to the valve. Residents living closest to the valve will get water first," the council said.
The authority said that anyone seeing white or cloudy water out of their taps should not worry - the water is safe to drink.
It said the discolouration is usually air in the water caused by disruptions to the network.
Meanwhile, meetings are ongoing involving Dublin City Council engineers and lab experts in their bid to resolve the crisis at Ballymore Eustace.
The experts are holding talks today on possible short term responses to the crisis but the council has already warned that restrictions will kick in at 8pm tonight regardless of any progress on the issue.
Michael Phillips, Dublin City Council engineer, is talking to various chemists and water treatment experts from overseas who have experience of similar treatment crises.
"What we need to do is find the people who have dealt with this exact, or more or less similar, situation before," a spokesman said.
Council lab technicians and engineers are at the Ballymore Eustace plant again today running through computer and physical treatment systems in a bid to identify the problem.
Hundreds of thousands of homes and business in Dublin city and county and parts of Kildare and Wicklow are 30 million litres below what is needed to keep taps and toilets flowing after the 10-day old problem.
Production at Ballymore Eustace has been cut by about a fifth.
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.
Experts have said the issue centres on sediment or treated material that needs to be removed from drinking water floating, or being suspended in treatment tanks, rather than sinking.