What must happen for the water dump light to turn off?

For the water dump light to turn off, the water dump button must be pressed again. This action serves as an indicator that the water dumping system is under control and has been manually reset by the crew. The purpose of the water dump light is to alert the flight crew that the system is actively in use, and pressing the button again signals that they want to discontinue the function or that they have acknowledged the alert.

In systems design, especially within the context of aircraft systems, many alerts or lights are designed to require a direct action from the crew to ensure acknowledgment and confirmation of status changes. Therefore, repeatedly pressing the button is a straightforward method to turn off the related warning light while also ensuring that the crew is aware of the status of the water dump operation.