Sinn Fein has accused Fianna Fail of acting in coalition with Fine Gael by abstaining in a motion to scrap water charges.
This gave Fine Gael a comfortable winning margin to push through the deal reached with Fianna Fáil during negotiations to form a new minority government.
Under this deal - water charges will be suspend for the moment, to allow for the establishment of an independent commission.
Sinn Féin TD Eoin O'Broin said Fianna Fáil has broken its promise to abolish Irish Water.
"They're supporting the Government and they're supporting this Government's policy, and they are supporting the continuation of Irish Water, despite clear election promises to the contrary," he said.
"And they're supporting a motion that leaves the door open to water charges in the future, so Fianna Fáil have to explain to their electorate why they promised to abolish Irish Water and water charges before the election and now are siding with the Government on these issues after the election."
Fianna Fail TD Niall Collins defended the decision not to vote against the abolition of Irish Water., saying his party plans to support future legislation to abolish water charges.
"There will be, through legislation, a suspension of water charges and a commission to look into the whole issue of water in this country," he said.
"So we've played a progressive part in this, unlike other political parties, and what we saw in the Dáil, spearheaded by Sinn Féin, the Anti-Austerity Alliance and indeed the People Before Profit was just simply petty politics."