Tánaiste Eamon Gilmore has confirmed that Labour will not sign off on water charges without allowances for families on low incomes.
He told the Dáil that €240 a year in water charges is too high a price for low-income households.
Taoiseach Enda Kenny is remaining tight-lipped on the growing gap between the two Government parties on the subject.
Deputy Gilmore says water is a "basic human right" - and the Government needs to act carefully to make sure nobody loses it.
"Shouting slogans at it doesn't resolve it," he said.
"It's making decisions that are based on the needs of people, ensuring that those who are on the lowest income are protected, that the burden is eased on them, and ensuring that families will be able to reduce their bill by water conservation."