Irish Water is seeking to reduce the proposed free allowance of 38,000 litres of water per child when water tariffs are introduced.
The company's intention was confirmed by Paul McGowan of the Commission for Energy Regulation at a meeting of the Oireachtas Committee on Environment, Culture and the Gaeltacht.
Mr McGowan said Irish Water is basing its proposal on research it has carried out on usage but the commission must be satisfied that research is robust.
He also said the commission has asked Irish Water to prepare for a minimum fee to be charged for water in non-primary residences, such as holiday homes. He said this will recognise that there is a cost for water even if no water is consumed.