Note: caffeine and alcohol are dehydrating in the body, so try to avoid them. If you do drink them during this re-hydration program, you would need to drink an extra glass or two of water just to gain back what you will lose. 2. Drink enough water daily. In order to rehydrate a dehydrated body, you need to drink at least one-half ounce per pound of body weight daily. So, for example, if you weigh 180 pounds, you would drink 90 ounces (about 3 quarts) of water. During exercise or hot weather, you should increase your water intake significantly, depending on how much you sweat, how long you exercise, or how hot the temperature is.
How pressure decreases with altitude. As you go higher in the air, the atmospheric pressure decreases. The exact pressure at a particular altitude depends of weather conditions, but a couple of approximations and a formula can give you a general idea of how pressure decreases with altitude.
Air gets 'thinner' with increasing altitude. That's why mountain climbers sometimes need bottled oxygen to breathe, and why it is so easy to get 'winded' while hiking in high mountains or even visiting someplace at elevation. Atmospheric pressure is around 1,014 millibars (14.7 pounds/inch 2) at sea level. At an elevation of 10 km (6 miles or about 30,000 feet), roughly the height of Mt. Everest, pressure drops to 265 millibars. That's less than 30% of the pressure at sea level! Both atmospheric pressure and the density of air decrease with altitude.