A confidential report from the European Commission indicates that it has concerns over Irish Water's finances.
Officials have warned of "uncertainty" surrounding the prospect of the utility passing the crucial market corporation test - which will determine whether the company can be kept off the Government's books.
The Irish Independent has reported that the document is critical of the Government's revised water package, which is capped at €160 for all households.
The EC report is concerned that a lower than expected revenue collection from the charge has "diminished" the prospect of Irish Water being self-funded.
Sinn Féin Finance Spokesperson Pearse Doherty TD said: “It was unbelievably arrogant or naïve of the Government to expect the EU Commission to see the so called water conservation grant as anything other than an exchequer transfer.
“Calling it a water conservation grant was only likely to deepen the bureaucrats’ suspicions.
“In December last year I raised this precise issue during the debate on the new water regime.
“The whole revised package is now in serious doubt.
“If the government’s plans fail the market corporation in test in April, I believe that the Government will then move to get rid of the water conservation grant altogether while pressing ahead with full water charges.
“The whole issue of Water Charges will not go away. The government can still abandon the concept of charging people for the water they drink and instead look at alternative models.
“I suspect the EU Commission’s concerns go even deeper than the grant. The message to Brussels should be that the Irish people have rejected water charges and that no tweaking of an accounting trick can change that.”