Minister for Housing, Local Government and Heritage, Darragh O'Brien, has said the failures identified in two water treatment plants are "unacceptable" as he ordered an audit of all such plants across the system.
The failures occurred at the Ballymore Eustace water treatment plant and at the Creagh water treatment plant serving Gorey in Co Wexford.
There have been 52 confirmed cases of illness associated with the Gorey outbreak, including bacteria linked to E coli, with a number of associated hospitalisations.
Minister O'Brien, in a post on Twitter, said: "I find the failures identified by the EPA unacceptable.
"People's confidence in our water supply is paramount. Immediate steps will be taken to ensure this does not happen again."
Speaking to RTÉ News earlier today, Mr O'Brien said the audit will initially focus on the 20 largest water treatment plants and is a "precautionary measure".
"I do want to say while these incidents are worrying, the water supply is safe," he said. "The water supply is safe in both of these areas but that does not get away from a situation where we've had systemic failures in process where public safety was put at risk."
He was speaking after a meeting with representatives of Irish Water, Dublin City Council and Wexford County Council this morning.
The minister said the issues arose through a combination of human error and not responding adequately when the issues were first identified.
"We cannot have situations like this reoccuring again," he added.
The Environmental Protection Agency, meanwhile, has said there could be further enforcement action, up to and including prosecutions, following the incidents where unsafe water entered the public drinking water supply at the two water treatment plants.
EPA Director General Laura Burke said there were unacceptable delays in notifying her organisation and the Health Service Executive about the incidents.
This meant that 900,000 water consumers were left unaware of the failures and did not have the opportunity to protect themselves.
Investigations at both plants revealed what the EPA described as "abject failure" of managerial oversight, operational control and responsiveness by Irish Water and local authorities in terms of their respective roles to deliver safe and secure drinking water.
The EPA investigation at Ballymore Eustace revealed that the plant produced unsafe drinking water for a period of up to 10 hours on 20 August to 21 August, due to the loss of the Cryptosporidium treatment barrier compounded by inadequate disinfection.
It is the largest water treatment plant in the country, serving approximately 877,000 consumers in the greater Dublin area.
The incident was not notified by Irish Water to the EPA or to the Health Service Executive until 1 September.
It prevented a timely risk assessment of the impact on drinking water quality and to allow interventions to be taken that could have protected public health.
The EPA investigation at the Gorey water treatment plant found that a power failure and a chlorine pump failure resulted in water leaving the plant and entering the public supply without the appropriate level of disinfection.
This went on for approximately five days between 19 August and 24 August.
General Manager of Irish Water Eamon Gallen said that in both incidents Irish Water and the local authorities who operate the water treatment plants on its behalf fell short of the standards required to protect public health.
In a statement today, Irish Water managing director Niall Gleeson said: "Irish Water agrees with the Minister and the EPA that both incidents are unacceptable. In both instances, late notification of issues relating to the disinfection process at the plants potentially put public health at risk.
"In discussions today with the Chief Executives of Wexford and Dublin City Council we reconfirmed that all measures would be taken to ensure there would be no re-occurrence of drinking water issues and can confirm to all customers the water is safe to drink."
Wexford County Council, meanwhile, said the problem at its water treatment plant at Creegh "only came to light on 26 August and was immediately discussed with Irish Water and the HSE."
In a statement issued to RTÉ News, the council said a chlorine dosing pump failure arising from an electricity power outage at Creagh Water Treatment Plant led to a deterioration of water quality due to inadequate disinfection over the period 19th to 23rd August.
It said once it became aware of the issue water quality information was examined by Council technical staff, Irish Water and the HSE and it was agreed that the incident had passed and the Water Treatment Plant was operating normally, with all network tests clear. Since the incident, the water quality in Gorey has been tested widely and extensively and again all network tests have been clear.
Dublin City Council said it is working to implement any necessary improvement plans at the Ballymore Eustace plant.
"DCC acknowledges that there was a failure in its reporting system at the time and is currently working with the EPA and Irish Water, whose recommendations will be implemented, to ensure that this does not happen again," it said.
"We wish to reassure the public that the breakdown at the plant was resolved some weeks ago and no longer exists."
Warning of consequences
Social Democrats co-leader Róisín Shortall said the water contamination in Dublin and Wexford are two very serious incidents and there will be consequences.
Speaking on RTÉ's Saturday with Katie Hannon, she said questions must be asked about the procedures that were followed and to set out the facts.
"Where was the breakdown between Irish Water and the local authority?", she asked.
She also said there is a need to find out why people were not notified.
Sinn Féin TD David Cullinane said it was unacceptable and that swifter action should have been taken.
He also made the point there is under-investment of waste water plants and that a lot of work has to be done to improve them.
Independent TD for Wexford Verona Murphy said guidelines were not followed and as a result people ended up quite ill.
She said it is incumbent on the CEO of Wexford County Council Tom Enright to restore confidence in the community following this incident.
She said she wants answers on why this happened and why a boil notice was not issued.
She said she had received calls from constituents about the issue at the time when they were feeling ill and had passed them on to Irish Water.
Additional reporting George Lee