THOUSANDS of homeowners already paying for their drinking water will be hit on the double when water charges are introduced.
Of the 170,000 households in a group water scheme, more than 50,000 already paying up to €100 a year will also have to pay a separate charge to Irish Water, the Irish Independent has learned.
This is because wastewater from their toilets and kitchen appliances, including washing machines, is discharged into public sewer systems.
It is not yet clear what the extra charges will amount to but it should lead to annual bills for water at least doubling.
Charges, which were due to be introduced next year but may be delayed until 2015, are made up of two components – 'water in', or drinking water, and 'water out', which is to cover the cost of treating wastewater.
These homes already pay for 'water in' by way of annual fees to a private group water scheme. They will now be hit for the 'water out' part when billing is introduced.
Up to six staff at the Commission for Energy Regulation (CER) will begin working on a billing and payment structure later this year. They will recommend the amount each householder will have to pay, and the final decision will then be taken by Government.
Irish Water, which will be responsible for billing 1.7 million households, said a "small" number of people on group water schemes would get annual bills.
Figures from the Central Statistics Office (CSO) show that 53,979 households draw their drinking water from a group water scheme but discharge into a public sewer.
"It is expected the charging policy will take account of situations where a customer receives either their water supply service or wastewater services from Irish Water, but not both," a spokeswoman for Irish Water said.
"Those customers will not pay the same charges as people who receive both water and wastewater services. A customer may be a member of a group water scheme or may have their own well but could be connected to the public wastewater system.
"The details of how the charges will be structured to take account of households who receive either a public water supply or public wastewater service, but not both, have yet to be finalised."
A spokesman for the Irish Federation of Group Water Schemes said average bills paid by households varied but that it was not be aware of any annual bills exceeding €100.
However, he questioned how their Irish Water bills would be calculated.
"The bills from Irish Water will be water in, water out," he said. "The bills from group water schemes are generally water in, because many people have septic tanks and look after those themselves.
"I wasn't aware so many households would be disposing into public sewers. How are you going to divide that up? How will they be charged for that?"
The amount of free water allocated to homes also varies between group water schemes before charges arise, he added.
Average water use per person in Ireland is almost 55,000 litres a year. In Monaghan, for example, each household on a group scheme gets 140,000 free litres before charges are applied.
The manager of one scheme in Co Galway said water usage dropped by up to 40pc when metered water charges were introduced.
Pat O'Looney, manager of the Loughrea Rural scheme, said each 1,000 litres cost €1, and that average bills ran to €88 a year.
"The metering of the system has cut down on a lot of waste," he said. "There was probably a 40pc reduction when all the meters were installed.
"People have been paying for years in a lot of rural Ireland."