Irish Water has confirmed that it has asked around 11,000 customers who submitted payment details in writing or over the phone to re-submit the information.

The company said that 9,000 customers who gave details of direct debit mandates over the phone were asked to re-submit them in writing, following concerns over data protection.

Another 2,000 customers who submitted payment details in writing were asked to do so again, because of what Irish Water described as "errors" in transposing customer details online.

The company said around 800,000 customers had registered in writing, far more than it had expected.

The utility will begin issuing the first quarterly bills to its 1.5m customers tomorrow.

The company has described the billing process as a significant task, and said it expects there will be errors in its database.

Staffing at a call centre in Cork has been increased to 750 to deal with customer queries during the initial billing period.

Staff at Irish Water and their customer service agents based at the Abtran call centre have been involved in a dry run on Irish Water's billing system for several weeks.

Today the system goes live and tonight the first 39,000 bills will be issued to customers across the country.

Billing is being rolled out on a phased basis over an eight-week period and during that time bills will be posted or emailed to every region of the country.

A total of 1.7m bills will be issued, including to those who are not customers of the new utility, such as to people on group water schemes.

Bills will not exceed €160 per year for single adult households or €260 per year for households with more than one adult.

For initial bills charges will not exceed €40 for a single adult household and €65 for a two-adult household.

Customers can still register with Irish Water until 30 June to ensure they are eligible to apply for the Government's Water Conservation Grant.

The grant will be available in September from the Department of Social Protection.