Labour party senator Lorraine Higgins said the 2nd February had never been a "drop dead deadline" for registering with Irish Water but said it was important " for the purposes of allowances" that people register on Monday.
Ms Higgins was speaking on RTÉ radio as the 'deadline' for registration with the utility by midnight looms.
There is no penalty for not registering by this time, but the default rate of €260 will apply to households with no confirmed details.
Senator Higgins said those who failed to register their details by midnight on Monday could see added costs on their water bills but was unable to say what these costs might be.
“The Department of the Environment has come out very clearly and said that there may be a situation where there’d be added cost on to the price of paying for water for this year,” she said.
Asked to specify the exact costs, she said that “hadn’t been clarified yet” and she was waiting to find out what they would be.
“ There will probably be a lot of discussion over the course of the coming week in relation to it.”
Asked what the penalties would be if people did not pay Irish Water bills when they begin arriving inApril she said there would be a ‘situation’ involving an exchange of information from the Revenue.
“We expect that there’ll be legislation brought in over the course of this month where it’ll be possible to put a charge on property. It’ll also be possible for landlords to bill their tenants and take it out of their deposits.”
Ms Higgins was unable to say how much of a charge should be put on people’s property if they do not pay.
“I can’t say that ... and I’m not going to speculate on that... I haven’t given it significant thought but I would urge people that it is important not to break the law. I wouldn’t be throwing it around, the populist line that Sinn Féin currently are,” she said.