A water utility shall, at the request of an authority, supply to the authority, on or before the 15th day of the month following the month during which water bills are issued, a list of all water meter readings and flat-rate water bills issued during the preceding calendar month and the basis of each flat-rate customer's water charge for use by the authority in calculating or computing its rentals, rates or charges for furnishing sewer, sewerage or sewage treatment service to the water customers.
53 P.S. § 3102.503