It shall be the duty of the City Manager, when required by the Council, and at least once in every five (5) years, to prepare or have prepared, with respect to any City-owned utility, an analysis of the plant investment, depreciation, obsolescence, reasonable return and operational costs, so that there can be determined therefrom the efficiency of the plant management and the reasonableness of the rates charged. Such analysis, when so prepared, shall be a public report and shall be incorporated and made a part of the minutes or journal of the Council.