Did you have a panic attack when you opened your water bill? Well,, it seems that there was an error that caused 13,000 bills to be mailed out with the incorrect amount. From the PWSA website —

If you received a bill dated January 6, 2010, PWSA is aware that it was not printed correctly. You will receive a corrected bill in the mail. If you do not receive a corrected bill by Tuesday, January 19, 2010, please call Customer Service at 412-255-2423. We apologize for this inconvenience.

The error was due to problems that a third-party vendor had with its software. There is some more information about that on the Pittsburgh Business Times.