Bills sent to residencies east of Airport Road and north of N.C. 54 failed to take into account payments customers had made since the last billing period.
OWASA realized the problem when a customer called the company regarding his statement.
"Some payments made were not posted correctly," OWASA Public Affairs spokesman Greg Feller said. "Some items were not shown as credited."
The error was caused by a glitch in the updating of the system software.
Kevin Ray, OWASA director of finance and customer service, said the company was unaware that updating the software would result in billing changes and that the checking system did not catch the error.
"Our normal procedures failed us," Ray said. "This is an application we've been using for several years."
Ray said that when OWASA officials heard of the problem, they quickly investigated but do not yet know the exact cause of the glitch.
"We've immediately taken a look at the procedure," he said. "It's difficult to say what the problem was."
Ray said OWASA is not responsible for printing the bills and that during every billing period, the printing company sends sample bills back to OWASA to be checked for error. Ray said the sample bills for this period were correct.
"The bills are printed by a third party," Ray said. "The small sample they returned did not reveal the glitch."
Feller said OWASA is working on updating the software so the problem does not occur in the future.
"Certainly, we don't like mistakes like this to happen," Feller said. "Of course we want to minimize that."
Despite the system error, Feller said that account statements in the OWASA office are up-to-date and that customers are encouraged to contact the office for the correct amounts.
"The records in our office are correct," Feller said.
"We are inviting people to call us for their balance."
Feller said customers who overpay will receive credit for future billing periods.
OWASA officials are notifying the residents of the error by printing a statement in newspapers and recording a telephone message for people calling about the problem.
Feller said OWASA has contacted the printing company responsible for the error and is in the process of correcting the system for the next statements.
"We are in touch with the company that manages billing," he said.
"We want to figure out precisely what happened."
Feller said he wants to emphasize OWASA's willingness to provide correct account information to residents.
"The main point is to apologize to customers," he said.
"We're glad to tell people their correct amount."
The City Editor can be reached at email@example.com.
To get the day's news and headlines in your inbox each morning, sign up for our email newsletters.