Just using a LOT of water is a bad idea (unless you eat a good amount, with salt and other nutrients around that time). Because as we all know, this can lead to hyponatremia (at the risk of stating the obvious: you sweat out a lot of salt with the water you lose. Only replacing the water dilutes your blood (serum).
As altitude  increases, the air becomes less dense because of the smaller amount  of air above that altitude. There is a corresponding decrease in  pressure with an increase in altitude. Eventually you reach a point  without air, and the pressure decreases to zero. That is space. + 91 others found this useful.
The decrease in barometric pressure with increasing altitude reduces PAO 2. PAO 2 decreases from 103 mm Hg at sea level to 81 mm Hg in Denver, Colorado (5280 ft [1609 m]) and to 48 mm Hg at the top of Pikes Peak (14,110 ft [4301 m]).s the altitude increases, barometric pressure decreases. This decrease in barometric pressure affects the partial pressure of alveolar oxygen (PAO 2). The percentage of oxygen remains stable at about 21%.