Irish Water has confirmed that it plans to send out water bills to more than 1.7 million households in the full knowledge that hundreds of thousands of those bills will be incorrect.
The company said it has to operate on the basis of incomplete information and that households will receive the bills over an eight-week period starting in the first week of April.
More than 700,000 households who are not registered will receive a bill.
This includes more than 150,000 households, which the company says are not customers of Irish Water, but who will receive a default bill because they have not yet provided information or registered.
The bills, which are quarterly, will ignore the Government's €100 water conservation grant.
For the first quarter they be will capped at just over €39 for a single adult household and €64 for a household with two or more adult.
All those who have not registered with the company are likely to receive a default bill of €64 for the quarter.
Speaking on RTÉ's Morning Ireland, Irish Water's Head of Communications Elizabeth Arnett said the bills covering the period from 1 January to 31 March would come over an eight-week period.
She said some people would receive bills in April, some in May and some in June.
Ms Arnett added "while the charge is €260 and €160 - the bill that you will receive will be just under €65 for a two-adult household with both water and waste water and just under €40 for a single-adult household with both water and waste water services."
Regarding meter readings, which will take place ahead of billing, Ms Arnett said at least a third of households, who have a meter, will pay less than the €65 or the €40 charge.
She said it was well worth having the meter and it is certainly well worth doing the meter reads.
She added some of the challenges arose out of non-unique addresses, saying that in such instances households would be sent correspondence and required to ring Irish Water to resolve the issue.
Irish Water says it has no choice but to operate on the basis of incomplete information and it is urging all those who receive incorrect bills to contact them to have the matter corrected as soon as possible.
It warned, however, that with such a new billing system many thousands of people are likely to receive incorrect bills.
For example, Irish Water knows how many people are on boil water notices and so should be entitled to some exemptions, but it does not have the names and addresses of the people in those areas.
It also says that thousands of people live at non-unique addresses where water meters have been installed but that it is very difficult in such cases to be accurate about how much each individual household should be charged.
In addition the company is warning that many households who have their own septic tanks could still receive bills that they should not get.
It said its call centre will be staffed by 750 people at its peak, and that it will remain open 24 hours-a-day to deal with the expected response to the bills in the coming months.
For billing queries the call centre will operate only between 8am and 8pm Monday to Friday and between 9am and 5.30pm on Saturday. Lines are closed on Sundays and bank holidays.
