The city of Watauga sent out notices this month asking residents to help repay an estimated undercharge of $400,000 covering six months of water billing cycles.
The amount varies per ratepayer but the city estimates it will require about an additional $40, payable over the next six months.
The letter says the city inadvertently charged thousands of customers a senior over-65 rate which lowered the bill for most customers a little more than $6 a month since July 2017.
Watauga City manager Andrea Gardner admitted the mistake has led to considerable frustration and confusion for ratepayers, but not recouping the money is not an option.
“It would be much easier for myself and staff if we could do that (not recoup the money) because then we would not receive the number of complaints," Gardner said. "But we have a responsibility to correct that."