New landlord Vicky Crawford has been inadvertently passing on the full Watercare Services bill to her tenants - unaware a portion of it was hers to pay.
"I had no idea," she said, when told of the matter this week.
"I've never been informed, I've never received any notification.
"I'd be surprised if anyone actually did know. It should be spelled out on the bill."
Crawford said she would reimburse her tenant for charges, and will ensure she subtracts the fixed charge from future bills.
"If you treat your tenants well, they treat you well.
"I think it's vital landlords pay back the money owed and ensure it doesn't happen again."
Crawford said she wondered why it had taken a year for Watercare to consider clarifying the bill, given the obvious confusion.