Paul Murphy TD says Irish Water is "engaged desperately in a rearguard action to try and defend themselves"
Irish Water has been warned that it may not be legally able to scrap charges.
Under European law there is no option to return to supply the service for free, according to legal advice received by the company and reported by the Irish Times.
Water charges are seen as a stumbling block to potential coalition talks between Fianna Fáil and Fine Gael who hold opposition positions on payment.
Reports at the weekend suggested that the deadlock may push the country towards a second election.
Anti Austerity Alliance TD Paul Murphy says the legal advice was commissioned by Irish Water after the general election.
"They're using public money - in what is the loss-making operation of Irish Water - to try to come up with arguments to keep something that people have just voted against," he argued.
Speaking to Newstalk Breakfast, Deputy Murphy also said he is not confident that Micheál Martin's party will stick to its anti water charges stance.
"I don't trust Fianna Fáil as far as I can throw them. They may be willing to negotiate away opposition to water charges in exchange for something else - Cabinet positions or whatever.
"The point is that we can't wait for them to negotiate a programme for government by themselves. The only way to ensure abolition is to... step up the boycott... and we need a massive united demonstration on the streets," he added.