That the board of directors may issue revenue bonds to finance the cost of constructing or purchasing revenue producing works and such bonds shall be a specific lien upon such works and the revenues derived therefrom and shall, in no case, be a debt that is guaranteed or secured by any other property within the district and no special election shall be required to authorize the issuance of such revenue bonds and such revenue bonds shall not be taken into account or in anywise be a limitation upon the power of said improvement district board of directors to issue bonds for any other purpose.