In the event that the board of water and sewer commissioners of any city (“commissioners”) should acquire, operate or control by virtue of assignment, conveyance, court order, operation of law or otherwise the water system of a water and fire protection authority (“authority”), then the commissioners shall conduct a study and adopt a plan within one year from the date that the commissioners shall first acquire, operate or control the authority’s water system providing for the construction of a sanitary sewer service system throughout the authority’s territory. The said plan shall be implemented and the improvements contemplated thereby constructed by the commissioners within five years from the date that the commissioners receive all necessary approvals (whether regulatory or judicial) and permits for the implementation and construction of an outfall line or any alternative sewer treatment or discharge facility capable of servicing the authority’s territory.