On the same note as my other question - another traveling question. Why does flying cause dehydration? How much water should I be drinking to combat this and does taking medication like Dramamine contribute to this problem?
Air Travel. At 30,000 feet (9,150 meters) the atmosphere inside a plane has to be artificially created. At that altitude, the cabin is pressurized to 8,000 feet, the equivalent of sitting on a mountain top, except for the healthy breeze. Outside air is too cold and too thin for us to breathe. So the aircraft ventilation systems draw in air and bring it to the correct temperature and pressure (by mixing hot engine air with outside cold air) and remove a lot of moisture, as high humidity can cause aircraft corrosion.
Also, your stomach expands at about 30% so you should stay away from large meals and try to consume a lot of water.