The county commission of the county issuing any such warrants may, in its discretion, assign and specially pledge for the payment of the principal of and interest on such warrants so much as may be necessary for said payment of any one or more of the following (or any part thereof):
(1) The proceeds from the general annual ad valorem tax of one half of one percent which the county is authorized to levy without reference to the purpose thereof under the provisions of Section 215 of the Constitution of Alabama of 1901;
(2) The proceeds from any other tax (including any ad valorem tax and any privilege, license or excise tax) that at the time of the issuance of the said warrants may lawfully be used by the county for payment of such principal and interest; and,
(3) The revenues derived by the county from any waterworks system of the county.
To the extent necessary and sufficient for making the payments in respect of which such pledge is made, any tax or revenues pledged pursuant to the provisions of this section shall constitute a trust fund or funds which shall be impressed with a lien in favor of the holders of the warrants to the payment of which such sums are pledged. In the event that more than one pledge should be made with respect to any tax or revenues the pledge of which is herein authorized in this section, then such pledges shall take precedence in the order in which they are made unless the proceedings making such pledge shall expressly provide that such pledge shall be on a parity with or subordinate to a subsequent pledge thereof.
All warrants for which the pledge authorized in this section may be made shall constitute preferred claims against that portion of the said tax or taxes or revenues so pledged (subject to any prior lawful pledges thereof in existence at the time of the issuance of the warrants, whether made under the provisions of this or any other statute) and shall have preference over claims incurred by the county for operation and maintenance of any waterworks system of the county and any other claims for any other purpose whatsoever.