That would mean that those with larger homes would face paying a higher water charge than those with smaller homes, when the new tax is introduced next year.
An “assessed charge” will have to be paid until water meters are installed and it is understood this will be based on the physical size of a home, rather than the number of people living in it.
It is thought the new charge could be as much as €400 a year.
Water meters are only expected to be in around 160,000 homes by the time the new charges come into force in 2014.
Installation of meters is expected to begin in July and proceed at a rate of 27,000 water meters per month, with the project expected to be completed within three years.