An Post must hand over personal addresses to Irish Water under new rules signed into law last week.
The Irish Independent has reported that Environment Minister Alan Kelly signed a statutory order that gives the company access to An Post’s database of addresses.
It is reported the move will ensure bills sent from next month reach the correct person.
Local authorities and other housing bodies will also be obliged to hand over private information on tenants to Irish Water under the new rules.
The move is expected to anger anti-water campaigners who already furiously fought a demand that Irish Water be allowed to collect the PPS numbers of all users.
Last November the company was ordered to delete all the PPS numbers it had collected from householders following angry protests on the streets.
The company has spent over €500,000 on campaign to encourage people to sign up for the hated charges.
The firm has spent €1.1million on advertising since it was created in July 2013 with €580,000 spent on a major campaign to ask people to get on board.
The figures released by the company are only the tip of the iceberg and do not include the cash spent on their latest campaign urging people to send their registration forms back.
The revelations will no doubt infuriate people who are due to take to the streets on March 21 in a protest organised by the Right2Water group.
Tens of thousands are expected to march despite the Government's revised plans and the release of four anti-water charge protesters from prison this week.
Richard Boyd Barrett said: "A massive demonstration will take place on 21 March which will put to bed the notion that the campaign against water charges is declining. There will be tens of thousands of people on the streets.
“Many of them, the ones who cannot pay, not just those who will not pay, will be council tenants and people in private rented accommodation on low incomes who already cannot pay the bills.
“They want to know will the Government have landlords and local authorities acting as boot boys, demanding with the threat of pay-ins, that these people pay these hated water charges.”
