Fianna Fáil has also reportedly proposed that charges be abolished
Dublin Sinn Féin MEP Lynn Boylan says legal advice she has has received confirms Irish Water charges can be scrapped.
This claim contradicts the view of the European Commission, which states that the charges cannot be removed.
Speaking from Leinster House, Ms Boylan said: "The legal opinion that I have received has confirmed what we have been saying all along, that the abolition of water charges would not contravene the water framework directive providing that Ireland can meet the objectives of the directive which is about the conservation and protection water.
"I welcome Fianna Fáil’s new found commitment to scrap water charges. Coming from the architects of water charges this is a major and welcome departure from Fianna Fáil.
"The majority of TDs elected to the Dáil in February were elected on anti-water charges mandates. Now that Fianna Fáil have accepted this there is a clear majority in favour of scrapping water charges.
"The expert commission is now redundant. It should be scrapped and the issue should be dealt with by the Dáil."
The legal advice, from Matthias Kelly QC and published by Ms Boylan, is summarised as saying: "Member States were free to determine, on the basis of an economic analysis, the measures to be adopted for the purposes of the application of the principle of recovery of costs.
"How the Directive was to be implemented was left to the Member State, so long as the steps taken did not impede or compromise the objectives of the Directive.
"There is a wide margin of appreciation. The Directive explicitly states that a Member State may have regard to its own economic and social considerations in deciding upon costs recovery."
Fianna Fáil has reportedly proposed that the water system be paid for through general taxation and that the principle of charging for usage should be permanently abolished.
The Irish Times says the party made the proposals in a statement to the Expert Commission on Domestic Public Water Services on how water services should be funded.
Its submission says the entire system should be funded through general taxation by way of direct subvention from the exchequer.
This marks a move away from its previous position, that charges should only be suspended for nine months.
While Green Party leader Eamon Ryan said: "Fianna Fáil’s u-turn on the issue of water charges is a return to populist economics, which will cost us all dearly in the end.
“In 2009 the Green Party and Fianna Fáil agreed to implement the recommendation of the Commission on Taxation to introduce a charge which would promote conservation of scarce water supplies.
"That commitment was written into our revised Programme for Government, without any objection from any of the Fianna Fáil negotiators. There was common agreement on the need to take investment in environmental infrastructure seriously, while protecting those on low incomes.
"Now Fianna Fáil are shamelessly backtracking in an attempt to win back electoral support from Sinn Féin and the AAA/PBP.
"Michael Martin has presented no economic, social or environmental argument for the u-turn they have made."