Irish Water says it will take a couple of billing cycles to resolve confusion over who is being charged and by how much.
The first round of bills will be sent out one week from today - and the utility is expecting a lot of calls from the public over queries about them.
Some 750 staff will be in place in call centres to handle the queries.
They include people being mistakenly billed, some meters that cannot be read because of technical issues, and problems with details like the number of people living in a house.
Meanwhile, the government announced a new deadline for registering for water charges last night.
Irish Water says they are building a database for the first time, and it is not unusual that there would be some 'teething problems'.
Elizabeth Arnett from Irish Water told Newstalk Breakfast that those who have their own water supply need to let the utility know.
Environment Minister Alan Kelly says households will have to register before June 30th - or else they will not qualify for the €100 water conservation grant.
Mr Kelly told TDs that more details about the grant, and how it would be paid, would be announced next month.