According to Bacheler, the human body loses about 8 ounces of water per hour on an aircraft at altitude, mostly from breathing. As such, the Aerospace Medical Association (AsMA) recommends drinking about 0.25 liters (or 8 ounces) of water per hour while on an airplane.

On an 11-hour flight, staying hydrated is crucial because the humidity in aircraft cabins is typically very low, often under 20%, which is drier than many deserts. For a flight of this duration, experts from the Aerospace Medical Association (AsMA) generally recommend drinking approximately 0.25 liters (about 8 ounces) of water for every hour you are in the air. For an 11-hour journey, this equates to roughly 2.75 to 3 liters of water in total. While this may seem like a high volume, consistent sipping helps counteract the accelerated fluid loss from your skin and respiratory system. It is also wise to avoid or limit diuretics like caffeine and alcohol, which can further dehydrate you. Bringing your own large, empty reusable water bottle to fill at the airport after security is a "pro" tip to ensure you have water on hand between cabin service intervals. Drinking small amounts frequently is more effective for hydration than "chugging" large quantities at once, and it also encourages you to move occasionally to use the restroom, which helps prevent deep vein thrombosis (DVT).