The energy regulator says the metering programme should be suspended
Irish Water has insisted it is delivering water services cheaper than the 34 local authorities were - but it cannot say by how much.
The Oireachtas Committee on the Future Funding of Domestic Water Services has also heard that the cost of billing customers is €25m a year.
The committee heard from the Commission for Energy Regulation (CER) that the metering programme should be 'parked' but not 'abandoned'.
It says investment should be focused on other areas.
But the idea of not having meters in every home appears to undermine the report of the Expert Group on Water Charges - which wants homes to be charges for excessive use.
Labour TD Jan O'Sullivan says without water meters, it will be possible to charge households who use water unfairly.
"To be quite honest I don't see any other way of establishing if people are overusing than by having meters.
"It seems to me that that isn't going to capture essentially how you would provide an adequate household allowance and then charge people who are over using".
Paul McGowan of the CER also says Irish Water's costs are excessively high.
"Irish Water at this stage of its evolution is a high-scot utility - we would expect that because it has inherited 34 different water authorities.
"But our analysis would indicate that they're up to twice the cost of an efficient utility, so what we will be doing over this revenue control and the following revenue controls is ensuring that they deliver the efficiencies to get down to the level of cost of an efficient operation", he added.
The CER has made a submission to TDs who are considering the future of the water network.
The committee is inviting major players in for hearings on the future of the scheme.
Earlier, doubts were raised over calls from the energy regulator to suspend the installation of water meters.
Irish Water has sent figures to TDs showing that around one-third of households use more than the average of 123 litres per person per day.
Anti-Austerity Alliance TD Mick Barry says if that is the agreed threshold - as Minister Simon Coveney has suggested - many households will still be hit.
"The Minister Simon Coveney has said there should be 123 litres per person, per day not charged and you pay on top of that.
"The Irish Water stats that come before the committee this afternoon show that a very large minority of households would still be hit for water charges if that system were put in place", he said.
Yesterday, MEP Brian Hayes called on the European Commission to make itself available to the Oireachtas Water Committee.
He suggested: “Any future system to fund our water services has to comply with the EU’s Water Framework Directive. This Committee needs clear legal advice from the Commission about what system does or does not comply with the Directive, if it is to make recommendations to the Dáil and Seanad."