The city shall not be bound by any deed or by any contract, unless the contract or deed has been authorized or ratified by ordinance of the council, or, where within the province of the board of water commissioners, by resolution of the board of water commissioners. Except leases of real property and the covenants and undertakings therein, no contract or franchise shall be entered into by the city binding it for a longer period than ten years; provided, that the city shall have authority to enter into contracts not exceeding twenty (20) years in duration with other municipal or quasi-municipal corporations for the construction, operation, or maintenance of public systems and facilities for domestic water supply or sewage collection or treatment or other public utilities to serve areas outside the city. The city shall not enter into any lease, as lessor or lessee, for a period longer than fifty years. No franchise shall grant any exclusive right or rights. This section shall not be construed to prevent the issuance of bonds of the city otherwise authorized for a longer period than ten years if, in the opinion of the council, such longer term will be for the best interests of the city, but no bonds of the city shall be issued for a longer period than thirty years.