The Government's rebate of €100 for every household on water charges will not be available until at least September next year.
By that time, householders will already have received two to three bills from Irish Water.
In a major climbdown by the coalition this afternoon, bills will be delivered at €65 every three months for families and €40 every quarter for single adult households.
The €100 "water conservation grant" will be administered by the Department of Social Protection, but will not be in place until late next year.
Meanwhile, Irish Water is being told it will have to differentiate between those who cannot afford to pay and those who will not.
Penalties will be applied to those who do not pay the charges, but Environment Minister Alan Kelly said those in financial difficulty would be worked with.
"Anyone who feels they will have issues with paying what are modest-enough charges - they need to be facilitated," he said.
"These are reasonable, decent people."