(1) Where there are contiguous or adjacent districts organized under the suburban improvement district laws or the municipal improvement district laws for either water, sewer or gas pipeline services, or any combination thereof, it shall be permissible for all or any two (2) or more of such districts, suburban, municipal, or any combination thereof, to enter into a contract with each other for the joint operation, maintenance, improvement, enlargement, and betterment of their respective systems or of the consolidated system, to be paid for by charges for the services.
(2) Any such district which has paid its outstanding bonds in indebtedness, but which has not been turned over to the municipality for operation, may join in contracts for joint operation.
(3) Any facilities constructed by any districts outside their boundaries shall be included in the consolidated systems.