Alabama Constitution of 1901, Art. XII, § 222.05

Revenue bonds or other revenue securities at any time issued by a county for the purpose of extending, enlarging or improving any water, sewer, gas or electric system then owned by such county shall not be deemed to constitute bonds or indebtedness of such county within the meaning of Sections 222, 224 or Amendment No. 342 [amending § 224] of this Constitution, if by their terms such bonds or other securities are not made a charge on the general credit or tax revenues of the issuing county and are made payable solely out of revenues derived from the operation of any one or more of such systems.