Some customers who paid their water charges will not receive their refunds by Christmas due to a Government delay in passing the required legislation.
The Taoiseach Leo Varadkar had previously pledged to ensure that all refunds would be paid by the end of the year.
On Newstalk Breakfast, Irish Water spokesperson Yvonne Harris warned that this is no longer possible.
“It is inevitable that some refunds will run into January because we cannot start until the legislation passes,” she said.
She said the utility’s objective is to begin issuing cheques “in the shortest time period possible” after it gets the go-ahead from Government.
Irish Water has today launched a dedicated page on its website to help householders receive their refunds.
For the most part, customers will not have to do anything to ensure they get their money back - however, the utility is advising customers who have moved house to contact them with their new address.
Ms Harris said the utility aims to issue 30,000 cheques per night once the process begins.
“Once legislation has passed we will be able to begin production of the one million cheques and we will be able to issue those quite efficiently,” she said.
“It also means that Irish Water will never ask our customers for bank account details by virtue of the fact that we will send the cheque to the account holder and the cheque is crossed.
"Only the account holder can cash that cheque.”
Water Charges have now been suspended for more than a year, with the Dáil having effectively abolished the controversial household charging regime.
Customers who paid all their bills will receive refunds of between €200 and €325.