HALF a million water meters have been installed across the country and Irish Water expects to have completed its installation programme by early 2016.
And data shows the location of the 20 houses found to be using a total of one million litres of water a day - the equivalent amount used by the 9,000 people living in Gorey, Co Wexford.
The homes are across seven counties and include one property found to be leaking an astonishing 89,000 litres of water a day - the equivalent usage of more than 600 people.
Householders were unaware of the problem, because the water was often flowing underneath driveways or gardens and never pooled on the surface.
Irish Water says that metering data analysed to date suggests that one in ten homes has a leak.
It comes as Bord Gais underestimated the cost of the metering programme by more than €100m. Figures provided to the Department of the Environment put the cost at €431.56m. But just weeks later it was revealed that the final cost would run to €539m.
Meanwhile, research shows that half of leaks identified by Irish Water involve faulty cisterns, where the toilet continually fills. The remaining leaks are in pipes leading from the mains to the property, meaning they will be eligible for the company's 'first fix free' policy that begins in January next year.
Some €51m has been set aside for the programme, but this figure is likely to increase as more leaks are located.
Because so many are minor in nature, it means that Irish Water will be able to advise householders on simple steps to eliminate the problem, which could be as minor as replacing a washer.
Irish Water boss John Tierney told the Irish Independent that the metering programme had provided valuable data on the extent of the leakage rates across the system.
Almost 50pc of all treated water was being lost, he said. This included leaks in the mains, and in private properties. But in some parts of the country an astonishing 70pc of all water was being lost. In one part of Roscommon, 72pc of all treated water leaks into the ground.
"One of the benefits of the metering programme is it shows changes in consumption patterns - that now means that the perceived leakage in the public system is higher than thought," he said.
"The metering still has significant benefits from the point of view of the information it's giving us on the system."
All Irish Water customers will pay an annual flat charge of €160 for a single person and €260 for a household with two or more adults until the end of 2018.
Each home in the State will also receive a €100 'water conservation grant' which can be used to install water-saving devices such as dual flush toilets, or to pay the bill.
However, where meters are installed and the amount of water used is valued at less than the flat charge, the household will receive a rebate.
The meters are being rolled-out in two phases - the first began in August 2013 and involves 1.1 million homes being metered by 2016. This includes 48,000 apartments which Irish Water believes can be easily metered.
The second phase will involve properties considered more difficult to meter, including terraced houses and apartments. Irish Water has examined various ways to meter these homes, and will seek permission from the water regulator in 2017 to carry out the works.