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 is made of molecules, and therefore has mass. Barometric pressure is a measure of how much mass of air, i.e. how many air molecules, exist above the point of measurement, all the way up to the top of the atmosphere. Therefore, barometric pressure decreases with elevation. Any given volume of air has density. The density of air can vary from place to place and from time to time. The difference in barometric pressure between observation sites at different elevations is a measure of the density of air in a column of air between those two elevations. Cold air is denser than warm air.