The Minister for the Environment has confirmed that 68% of septic tank owners have registered ahead of Friday evening’s deadline.
Phil Hogan said he expected that figure to increase to between 70% and 75% in the next 24 hours.
Mr Hogan warned that those who fail to register in time will be breaking the law and they would not be entitled to financial assistance if they have a problem with their septic tank in the future.
The minister also ruled out any extension of the deadline.
In relation to water charges, Mr Hogan dismissed media reports that they would be based on property size and said that they would instead be based on water usage.
He was speaking at the opening of the Shanganagh Wastewater Treatment Plant in south Dublin.
Protesters gathered at the site to voice their opposition to water charges, the household charge and the property tax.
In response to the protests, Mr Hogan said there would always be people who would not want to pay for anything.
Mr Hogan was also critical of Sinn Féin's opposition to these charges in the Republic of Ireland, when it asks people to pay service charges in Northern Ireland.