Whenever any of the property of a utility under the control of a metropolitan utilities district, whether real property or personal property, is no longer required for the operation of such utility, the district may sell and convey such surplus property, whether the property was acquired directly by the district or as a part of the utility plant or system acquired by the city of the metropolitan class or any municipality or other political subdivision constituting a part of the district. Proceeds of the sale of such surplus property shall be credited to the utility of which the property was a part, or when funds of more than one utility have been invested in property involved in a consolidated operation of the district, proceeds of such sale shall be apportioned among the utilities involved in such consolidated operation upon some reasonable basis determined by the board of directors of the district.