No indebtedness on the general credit of the municipality shall be deemed to be incurred by reason of any covenant or agreement contained in said contract or in the resolutions of the city with reference thereto. No revenues received from taxes or any other source, other than the revenues derived from said plant as hereinabove provided, shall be pledged for the payment of any contract executed or revenue bonds or certificates issued under the provisions of section 40-33-17 through 40-33-21. Such contract, bonds, or certificates shall not constitute a lien or charge on any property of the city, except that if the contract price is not paid by the issuance of revenue bonds, title to the plant or any specified portion thereof may be retained by the contractor as security for the purchase price, with right of repossession in the manner provided for property sold under a conditional sales contract, until full payment of the purchase price.