The Tánaiste Joan Burton has told the Dáil that the timeline for the establishment of Irish Water was "too ambitious".
It is seen as another signal from the Coalition that changes may be made to billing for water.
Last night Fine Gael TDs were told at their weekly meeting that the capped flat charge that is in place for nine months may be extended to the end of 2016.
Ms Burton has also said she does not accept that Irish Water will pay bonuses to staff in the start-up phase.
She said: "I do not anticipate any bonus payments or any enhancement payments, or whatever management speak is used on the payments, being paid at all until such time as the company is operational."