Where is the water level displayed in the aircraft?

The water level in an aircraft is typically displayed on the aft flight attendant (FA) control panel. This location is designated for cabin crew use and indicates the amount of water available in the aircraft's water tank, which is crucial for operations, including the preparation of in-flight services and for the use of lavatory facilities.

The importance of monitoring the water level is significant for maintaining adequate supplies for passenger needs, such as restroom facilities and beverage services. The aft FA control panel is specifically designed to provide the necessary information to flight attendants without requiring them to access the cockpit or intrude upon the pilot's space.

Other choices do not provide the relevant context for the water level display as they focus on locations not intended for cabin service information. The main flight display, passenger information screen, and cockpit are not typically used to show the water levels, as this information is specifically tailored for flight attendant management in the cabin area. Thus, the aft FA control panel is the correct answer for displaying the water level in the aircraft.