(a) Included amounts.— The monthly, quarterly or annual rental may include:

1. (1) The amount expended monthly, quarterly or annually by the borough in maintenance, repair, alteration, inspection, depreciation or other expense of the sanitary sewer, sewer system or sewage treatment works.
2. (2) Interest on money expended or borrowed by the borough in the construction of the sanitary sewer, sewer system or sewage treatment works or in the acquisition, enlargement or extension of the sanitary sewer or sewer system.
3. (3) An amount sufficient for the amortization of debt incurred by the borough for the purpose of construction of a sanitary sewer, sewer system or sewage treatment works or for the purpose of acquisition, enlargement or extension of a sanitary sewer or sewer system.