A system for converting a mechanical main valve body of a shower assembly to an electromechanical main valve body. The system includes a mechanical valve body that includes a cold water inlet, a hot water inlet, and a connection interface that interchangeably receives one of the mechanical main valve body or the electromechanical main valve body. The electromechanical main valve body includes a first solenoid valve fluidly coupled to a first outlet that directs the mixed water to a first user device in replacement of a second outlet of the mechanical main valve body, and a second solenoid valve fluidly coupled to a third outlet that directs the mixed water to a second user device in replacement of a fourth outlet of the mechanical main valve body. The first and second solenoid valves selectively permit the mixed water to flow through the first and third outlets, respectively.