A campaigner says a pipeline from the River Shannon, to carry water to other parts of the country, is simply not needed.
It comes as Irish Water says the only viable option to keep drinking water flowing in Dublin - and large parts of the east and midlands - is to fund the controversial pipeline in Co Tipperary.
The details are part of a public consultation on improving the water supply for more than half the country.
The plan includes 134 separate water supplies, catering for 2.5 million people, with the aim to support growth and reduce leaks.
Lawyer Emma Kennedy, of Kennedy Analysis, told Newstalk Breakfast pipes have to be fixed regardless.
"We have been opposed to it, along with the various other organisations, who have been challenging it for years and years.
"Principally because the pipeline is simply not needed.
"They're talking about extracting water from the River Shannon, pumping it 200 kilometres across the country through an enormous pipeline to Dublin - where leakage levels are off the charts."
She says Irish Water know most people are opposed to the plan "morally and for environmental reasons".
"Yet again they're coming out and their key fightback is to say 'Oh no, we're looking to do everything that we possibly can to reduce leakage. But even if we reduce leakage, we still need this pipeline'.
"Irish Water, they're very economical with the truth when it comes to talking about leakage.
"So for example, they're talking today about that fact that their plan to reduce leakage to levels that would be considered acceptable.
"For what it's worth, whenever they talk about leakage... that doesn't include a single drop of leakage from your house or from inside my house.
"That's purely leakage on their side".
And she says the money involved is climbing higher.
"From a taxpayer's point of view, spending €1.5bn and rising - right now it's 1.3bn, it started off at I think at about 650m - on this project means that €1.5bn is not available for projects that are genuinely needed.
"The pipes need to be upgraded in any event".