HOMEOWNERS face the prospect of getting hefty bills for water they never use.
Some private homes are consuming more than 120 times the average because of leaks in their plumbing systems, it has emerged. And local authorities believe at least 5pc of all homes have leaks in their pipes which take water from public supplies.
This means 70,000 homeowners will pay higher than expected water charges when they are introduced next year unless they carry out expensive repairs.
Average household use is estimated at 500 litres a day but a study by Galway City Council says some homes in its areas are using as much as 61,000 litres.
If charged at the current commercial rate, a Galway household that is using excess water would end up paying an annual bill of €46,941. This is 134 times what is expected to be the "average" bill of €350 a year.
Water charges are due to be introduced in summer 2014, with charges set by the Commission for Energy Regulation (CER). It is not yet clear if grants will be available to homeowners to undertake repairs, or if insurance companies will foot the bill.
Experts said the leaks problem was expected to be rife across the country, with research by Dublin City Council suggesting about 6pc of all homes in the capital have leaking pipes.
It has installed 1,100 water meters on 140km of new water mains, which allows it to monitor the amount being lost in private homes.
"The people who are involved in rehabilitating the mains tell me about 6pc of houses may have a problem," spokesman Tom Leahy said.
"Galway and Dublin would be typical of urban situations, and leaks are often found under the front garden or the driveway."
Limerick City Council also confirmed it has written to 200 homeowners in the last six months, informing them their pipes were leaking.
Sources said the situation was likely to be broadly similar in rural areas.
This means that of the 1.35 million homes which will be metered for water, some 70,000 properties could require repairs.
Some 43pc of all drinking water is lost because of illegal connections and leakage in water mains and private pipes.
Irish Water, the company charged with billing domestic customers, said reducing leakage across the network would be a "critical task", but that it would not know the extent of the problem until it took ownership of the water system next year.
However, a spokeswoman said homeowners would be responsible for fixing leaks on their property. Households which refuse to fix a leak can be fined up to €5,000.
A spokesman for Galway City Council said it believed one in 10 of all homes had leaking pipes.
It identified 10 properties which were using 341,000 litres a day – which would result in annual bills of €261,768.
Director of Services Ciaran Hayes said the council had written to the affected homeowners, and about half had already fixed the leak.