Update 11.40am: Irish Water has been accused of institutional arrogance by Tipperary TD Mattie McGrath.
It comes after the utility announced its intention to proceed with pumping water from the Shannon to supply parts of the Midlands and the greater Dublin area.
Deputy McGrath has called the project a billion euro error of judgement.
Irish Water's head of asset management, Sean Laffey, says they are simply running out of options to serve customers.
"The most we're very going to get out of the Liffey system is roughly 650 megalitres a day," he said.
"The average demand currently is 577, so the water simply isn't there in the Liffey system, it's no longer an option so we had to look at other options.
"We looked at groundwater and we looked at desalination, and then we looked at the Shannon and the Shannon is the option that we have chosen."
Update 8.14am: Irish Water is pushing ahead with a €1.3bn plan to bring water from the Shannon river to Dublin.
The law has yet to be updated to allow it happen, as the Government wants public consultation on it first.
The project would see water pumped from the Parteen basin in north Tipperary to the Midlands and Greater Dublin area.
The estimated cost has tripled since the original plans and is already more than a year behind schedule.
- Digital desk