(a) Rates for water fixed precedent to the issuance of the bonds shall not be reduced until all of the bonds shall have been fully paid and shall, whenever necessary, be increased in an amount sufficient to provide for the payment of the bonds, both principal and interest, and to provide proper funds for the depreciation account and operation and maintenance charges. However, the rates may be reduced subject to any conditions which may be set out in the ordinances authorizing the issuance of the bonds or in the trust indenture authorized under the provisions of this subchapter.
(b)
(1) If any surplus shall be accumulated in the operating and maintenance fund of any one (1) of the several municipalities which shall be in excess of the costs of maintaining and operating the waterworks system of that municipality during the remainder of the current fiscal year and the costs of maintaining and operating the waterworks system of that municipality during the next fiscal year, then any excess may be transferred to either the depreciation account of the waterworks system of that municipality, or to the bond and interest redemption account, as the several legislative bodies may designate in their respective ordinances.
(2) If any surplus shall be accumulated in the depreciation account of any waterworks system of any one (1) of the several municipalities over and above that which may be necessary for the proper replacements which may be needed during the fiscal year and the next fiscal year, that excess may be transferred to the bond and interest redemption account.
(3) If a surplus shall exist in the bond and interest redemption account, the same may be applied by the legislative bodies in their discretion subject to any limitations in the ordinances authorizing the issuance of the bonds or in the trust indenture:
(A) To the payment of any outstanding unmatured bonds payable from the bond and interest redemption account that may be subject to call for redemption before maturity; or
(B) To any other municipal purpose.