Make sure that your drink a lot of fluids when you are skiing even if you're not thirsty. A body that is put to work at an altitude of 2000-3000 meters (6000-10000 feet) needs at least 2-3 liters (2-3 quarts) a day. When active, you need more liquid than normal. A combination of high altitudes and physical effort can easily lead to dehydration.