HOMEOWNERS face the controversial prospect of paying for their water based on the size of their home, rather than their estimated usage.
People with bigger houses face paying a higher temporary water charge than those with smaller homes from next year.
The Irish Independent has now learnt an "assessed charge" – which will have to be paid until water meters are installed – is likely to be based on the physical size of a home, rather than the number of people in it.
Sources involved in establishing the water tax say this is because it will be "impossible to police" the number of people living in a home, and it said "it is moving the way of property type".
The charge could be as much as €400 a year, but "nobody will pay a flat rate", one source said. Information on properties – and the initial tax to be paid – could be gleaned from databases that exist from the €100 household charge and the property tax, once it has been fully established from this summer.
Irish Water, the new body set up to collect the charges, will have access to records held by the Revenue Commissioners and the Local Government Management Agency.
However, the exact cost of the assessed charge and water metering will be decided independently by the Commission for Energy Regulation.
The bailout agreement with the troika compels the Government to bring in water charges next year. But the process of installing the meters only gets under way this summer, and will not be complete for three years.
To meet the terms of the bailout, the Government will have to bring in the assessed charge – but sources say this will almost certainly be pushed back until after the local elections, not scheduled to take place until mid-2014.
"It is a matter for the Government to decide the date it will be introduced," one source said.
It is hoped as many as 500,000 meters will be installed by the summer of 2014.
The Irish Independent has also learnt a "lead-in time" for metering is being considered.
Under this proposal, being discussed in the Department of the Environment, homeowners will be able to monitor their water usage on a meter for a few months before paying the metered charge.
"That way, people could see what they'd be paying, and might be shocked by their bills," a source said.
Irish Water will also be allowed access to the Department of Social Protection records, and it is understood certain welfare recipients, as well as people with acute medical needs, will not pay the full amount of the charge.
And it is now thought apartment blocks will have one meter installed which will measure the usage of all occupants – then the charges will be divided up per apartment.