Householders will receive an information pack from Irish Water next month requesting details on water services, allowances and the number of occupants in every home.
The form is to be filled out and returned to the company by the end of October.
Domestic water charges will apply from October 1, and the first bill will come through the letterbox in January, with bills every subsequent quarter.
Elizabeth Arnett, Irish Water Head of Communications explains what happens if you don't return the form by the deadline.
She said: "If we don't hear back from people, we still have to send out bills. We'd prefer to do that to the right address with the right allowances.
"If we don’t hear back from people, for whatever reason, we have to make an assumption then in relation to the water usage, and we have to make an assumption in terms of the number of people in the house."