Watercare Services has received 765 complaints since radical changes on July 1 to the way Aucklanders pay for water.
The Auckland Council-controlled agency introduced monthly billing and a standard wastewater tariff based on a more expensive fresh water supply through the meter.
Information requested by the Herald shows the main complaint was the new tariff and charges.
Aucklanders were used to paying three-monthly or six-monthly bills but now get bills every month, sometimes based on estimates of use.
Customers were unhappy about being moved from wholly fixed charges for waste water to paying a $190 fixed charge plus 78.5 per cent of the home's metered use of fresh water.
North Shore, Waitakere, Rodney and Franklin residents did not understand that waste water charges no longer came out of their property rates bill from the council but were now charged directly by Watercare.
And fresh water was 3.3 per cent more expensive from July.
A Watercare spokesman said 559 of the complaints were about the July 1 changes - rather than errors in billing - and had been easily resolved by explaining the changes.
Where billing errors were found, accounts were credited immediately.
However, West Auckland landlord Gary Osborne believes people should read their monthly bills closely, because of his two experiences.
An estimated reading for the August bill on his rental property was way out of kilter, he said, and this happened again.
He pointed out the inconsistency of being charged $74.48 in October and $15.64 in November.
Watercare apologised for mistakenly increasing the billing period for the property to 41 days instead of the standard 29 to 30 days.
The daily water use was also wrongly calculated - resulting in a high reading of 390 litres a day instead of 300 litres for the 41-day period.
Watercare said that even with checks and audits of invoices, a very small percentage of errors occurred.
The spokesman said the customer centre would regularly review any customer whose accounts had repeat errors.
The Water Utility Consumer Assistance Trust, which was set up in January to help people who cannot settle overdue bills, has 144 applications that meet certain conditions and have been assessed by a budgetary advisory service.
Auckland water bills
*July 1, 2012 changed billing, tariff and charges
*2 million invoices issued
*559 about new tariff and charges
*0.18 per cent of customers complained
*177 seeking help to pay