The 39,000 bills that were issued overnight are the first of 1.5 million quarterly bills that will be delivered over the next eight weeks. This allocation will see people in Donegal, Meath and Wexford receive bills.
Irish Water has been metering water usage since January, and today, the utility company begins charging its customers for that water consumption.
Staff at the Abtran call centre in Cork are expecting thousands of calls from customers with queries and complaints as Irish Water's billing system goes live.
Bills for households with one adult will be no more than €40, while households with two adults face a bill of €65 or less.
Irish Water has acknowledged mistakes were made when the details of 2,000 customers were transferred online.
Another 9,000 customers who gave details of direct debit mandates over the phone are being asked to re-submit them in writing, following concerns over data protection.
