Where the improvement shall be ordered and payment therefor made without the issuance of bonds, the City Council shall cause warrants to be issued in payment of the cost and expense thereof, which warrants shall bear interest at a rate not to exceed eight percent per year, and shall be payable only out of the special fund to be provided for under the local improvement district under which the same is issued. [Code 1970 § 14.04.100; Code 1954 § 2-12.40.]