WATER meters could be installed in 300,000 properties whose owners were supposed to pay an "assessed" charge based on average consumption.
Irish Water will conduct a series of trial installations in Dublin apartments to see if it is technically feasible to install the meters, the Irish Independent has learnt.
Just over one million meters were due to be installed up to the end of 2016, with 300,000 houses and apartments outside the scope of the metering programme because of technical difficulties.
They included shared water mains pipes running into the units, or multiple pipes servicing the home, which could have resulted in a number of meters having to be installed to provide an accurate reading on consumption.
It was believed that this would be technically complex and expensive, so it was decided to bill these property owners on the basis of an assessed charge, to be calculated on average consumption and decided by the independent regulator, the Commission for Energy Regulation.
However, Irish Water and the Department of the Environment have now decided to examine if meters can be installed in these units.
"The plumbing configuration in apartment blocks can vary greatly depending on the age or nature of the apartment block," a spokeswoman for Irish Water said. "In certain circumstances, apartments may not be self-contained in terms of plumbing or they may have multiple water pipes running into the apartments.
"Irish Water has recently commenced a study to determine the feasibility of installing meters in apartments and multi-unit dwellings. It is expected that this study will be concluded in the second quarter of next year.
"This study will include a number of trial installations in a range of apartment blocks in Dublin, in which technical solutions for metering apartments and multi-unit dwellings will be tested."
Some 27,000 meters a month are due to be installed in homes across the country over the coming years, and if it is decided to meter apartments it will extend the programme for another year.
One of the largest metering programmes ever conducted, some 1,400 construction jobs will be created. Five hundred of these jobs are already in place, with the remainder to come on stream before year end. The contracts with construction companies require that 25pc of staff are drawn from the live register, local businesses and school leavers. Irish Water says this figure now stands above target at 40pc.
Work began on the metering programme in Kildare last August, and some 6,500 have already been installed in Kildare, Kerry, Meath and Wexford. Metering in Dublin starts next week, moving to Limerick and Mayo by the end of the month. Meters will be installed in homes across all 26 counties by the end of the year.
Separately, the Department of the Environment has said it plans to oblige developers of new apartments to install water meters in each unit so individual bills can be sent.