Comments come as 39 opposition TDs call for immediate end to water charges
Fianna Fail says it is not in the business of saying one thing, and then doing another.
The claim came as the party resumed its talks with Fine Gael, hoping to reach agreement on a minority government.
Negotiations are continuing in Trinity College this afternoon, with hopes that a deal could be reached over the weekend.
Irish Water remains a key area - and Fianna Fáil's Michael McGrath says the party is not preparing for a U-turn on its election promise to suspend water charges for five years.
Meanwhile, four opposition parties have meanwhile tabled a joint motion calling for an immediate end to water charges.
The motion - signed by 39 TDs - will be debated after a government is formed, but Catherine Murphy of the Social Democrats says the decisions on Irish Water should be taken immediately, in the Dáil.
The comments come as Fine Gael and Fianna Fáil return to Trinity College Dublin for negotiations on the formation of a minority government.
Fianna Fáil have called today a 'pivotal day' before a possible deal in the coming days.
Acting Health Minister Leo Varadkar also says he is hopeful of reaching a final deal over the weekend.
He was asked if trust between the two parties was a barrier to making progress.
It was suggested yesterday that the parties were close to an agreement on government formation, after reaching a compromise on suspending water charges until a fairer system is brought in.
It was also reported that a deal between the old rivals could be signed off by the weekend, paving the way for Independents to decide if they want to be included.
However, Fianna Fáil TD John McGuinness says the party is sticking to its election promise that Irish Water would be abolished.
Speaking on Newstalk Breakfast earlier, Deputy McGuinness explained: "There's two very different positions here. In supporting a Fine Gael in a minority position, I think the members of the parliamentary party want to be absolutely clear on where exactly we're going".
"But we're reading reports in the media that can't be reconciled with with the position that we're taking in the parliamentary party meeting," he added.
The reported deal was said to have indicated that the commercial semi-state would go into full public ownership as a state company, with charges suspended until a fairer regime could be put in place.
That led to a cool reception from Fianna Fáil TDs, who said it did not meet enough of what they promised in the election.
Last night negotiators insisted they had not even discussed the issue of water charges yesterday.
The talks have now resumed and both sides insist discussions will continue throughout the weekend if necessary.