Irish Water said the highest bill they have seen so far was close to €20,000.
Water bills are capped at the moment, but where households are metered, customers’ bills will show the monetary value of the water they’ve used.
Where bad leaks are present, that figure can be astronomical.
"We have seen some bills up as far as just short of €20,000," said Yvonne Harris, Billing services manager with Irish Water.
"If a customer looks at the back of their bill, the metered consumption is displayed on the back of the bill.
"Our bills are capped at [about] €64 for each quarter. If a customer finds that the monetary value of the metered consumption is excessive, that would definitely indicate that they have a leak."
She said anyone with an unusually high bill should contact Irish Water's call centre.