Two incidents of water contamination that led to 52 confirmed illnesses were caused by “late reporting issues”, Irish Water has said.
Managing director Niall Gleeson apologised for the “serious failures” before an Oireachtas Committee on Thursday.
He said the incidents had shown that the current arrangement, where the utility works alongside 31 local authorities, is “not fit for purpose”.
Irish Water is to carry out an audit of all water treatment plants across the country, after serious incidents at drinking water facilities at Ballymore Eustace, which serves parts of Dublin city, and Gorey in Co Wexford.
Mr Gleeson said: “I would like to apologise again for both incidents.
“While equipment failure and human error can occur, late reporting of issues relating to the process failures at the plants, left us unable to react and compromised water quality.”
Mr Gleeson told the committee that on Friday, August 20, disinfection processes failed at Ballymore Eustace Water Treatment Plant.
He said Dublin City Council, which operates the plant on behalf of Irish Water, did not report the incident to them at the time it occurred.
He added: “The issue came to light on August 30, on investigation of related issues at the sludge treatment facility at the plant.
“As soon as Irish Water became aware of the issue, it notified the HSE and, as the incident had passed, immediate public notification was not required.”
At the plant in Gorey, the disinfection process was compromised between August 19 and 24, and dealt with by Wexford County Council on the August 24.
Irish Water were informed of the incident on August 26, Mr Gleeson said, and immediately notified the HSE and the Environmental Protection Agency (EPA).
He added: “The HSE advised that a boil water notice on the supply was not necessary at this point as the incident had passed and the plant was operating correctly.”
However, in the following days Irish Water received several complaints relating to water discolouration and reports of illnesses in the Gorey area.
Mr Gleeson said: “The HSE also confirmed that there were reports of multiple illnesses in the community.
“Irish Water issued an update to elected representatives in the Gorey area and updated our website advising customers that an issue had occurred and to contact their GP if they felt unwell.”
Mr Gleeson said that as a result of these incidents, the current arrangement, where Irish Water works alongside 1 Local Authorities to deliver water services, is no longer fit for purpose.”
He added: “The issues that have arisen at the water treatment plants in Dublin and Wexford clearly show the limitation of the present ways of working and emphasise the urgent need for change.
“Irish Water has legal responsibility but no direct control over water treatment plants around the country.”
Mr Gleeson said it is “critical” that a move to a single public utility is progressed “as a matter of urgency”.
Feargal O Coigligh, assistant secretary in the water division of the Department of Housing, said “the limitations of that model are clear”.
He added: “A process has commenced under the WRC (Workplace Relations Commission) to seek agreement on new arrangements which give Irish Water full control of service delivery.”