Potable water must be serviced during every:

The servicing of potable water is typically required during the arrival of an aircraft. This is essential to ensure that the onboard water supply meets safety and health standards for passengers and crew. Upon arrival, it is standard practice to check the water levels and replenish them as necessary to maintain hygiene and compliance with regulations.

Maintaining adequate potable water supply is crucial for comfort, hygiene, and operational regulations within the aviation industry. Water service is not necessarily linked to every flight departure, maintenance check, or emergency landing, as those situations might not demand immediate replenishment of potable water. Instead, the focus remains on ensuring that the water supply is adequate for the next departure and that the aircraft is ready for future passengers. Therefore, service during arrival is the primary moment designated for this task.