A spokesperson for Irish Water has said it is very difficult to speculate about the potential range of household bills for water charges.

Speaking on RTÉ's Morning Ireland, Elizabeth Arnett, head of Communications and Corporate Services with Irish Water, was responding to questions about the potential for people having to pay above the predicted average bill of €240 a year.

She said the price per litre of water is not known yet, and this will be determined by the regulator.

She said when people start paying for water they start changing their behaviour in terms of the amount of water they use.

Ms Arnett said the majority of households will not have metres installed by the time billing starts in October this year.

Asked about the possibility of water charges going up in the future, Ms Arnett said she could understand the concerns people have about this.

She said it was very difficult to say what would happen beyond the price-control period which runs until the end of 2016.

She said Ireland was good at attracting investment from the market for utilities, and that this investment lifted the burden off the exchequer and the taxpayer.

Meanwhile, a former CEO of Northern Irish Water has said it is unusual that there will be no standing charge for water under Irish Water's new payment scheme.

Trevor Haslett said the cost of a standing charge was intended to cover the cost of installation and maintenance of the metre, and the fact that a household was connected to the mains.

Mr Haslett said not having a standing charge was unusual in terms of the UK and Europe across any utility.

He said it was considered the most equitable way of raising funds and charging for water.

He said it was obviously a political decision not to have a standing charge.

Asked about the average cost of water to households, Mr Haslett said he believed a significant group of customers would end up paying more than the predicted €240 average annual household water charge.

He said in the UK the average annual charge is £388.

Mr Haslett said there was no detail on the level of government subsidy being provided to Irish Water for two years, and he said people had been asking what would happen in January 2017 after the period of the subvention.