Irish Water failed to respond to a number of warning signs that there was a problem at the Leixlip Water Treatment Plant, a senior EPA officer has said.
Environment Protection Agency Programme Manager Andy Fanning said there had been previous warnings about the issues by the EPA following an audit of the plant in May.
Around 600,000 people were placed on a boil water notice in parts of Dublin, Meath and Kildare last week over issues with the treatment process at Leixlip, which may have compromised the disinfection process making the water unsafe to drink.
The notice was lifted last Friday.
Speaking on RTÉ's Morning Ireland, Mr Fanning said the EPA audited the plant earlier this year, identified these problems and informed the Irish Water there must be "automatic shutdown" if those alarms were not responded to in an appropriate time.
The audit found there was a blockage at the treatment plant, which was made up of small black particles or debris originating from two storage tanks that are approximately 25 years old.
Deterioration of the tanks' internal lining resulted in flakes being drawn into the pumps and then into the dosing line, which caused the blockage.
Mr Fanning said the EPA was assured by Irish Water that it had put systems checks in place. However, these checks were only put in place in one part of the plant, rather than three.
Mr Fanning said the utility has been put on four weeks' notice "to get their responses in order" and explain to the EPA what it will do next.
Mr Fanning assured people that the water is fit to drink now, but said enhanced treatments at plant are needed to safeguard supplies in the future.
Minister for Social Protection Regina Doherty said she was very concerned that corrective actions after the March review of the Leixlip plant by the EPA were not fully implemented.
Minister Doherty said: "It's a bit Irish in this day and age that people have to boil water as a result of what potentially is missed recommendations from a previous review."
Minister for Housing Eoghan Murphy said he is to meet the heads of Irish Water and Fingal County Council to discuss the findings of an EPA audit of the treatment plant.
The minister said it was very alarming that "fail safe procedures had been put in place at the plant but hadn't been working".
Mr Murphy said the incident that led to the boil water notice should not have happened, and that any necessary works would now take place to ensure a similar problem did not arise again.