The South Pole is around 9500 ft and the air pressure is much lower here, so the effective altitude is around 12000 ft above sea level. This takes some getting used to, and can even be life threatening. As an example, once I got to my sleeping area (a curtained-off cell in a Quonset hut at "summer camp"), I made my single bed. After I made my bed, I had to sit down for 4-5 minutes to catch my breath!
Antarctica is also one of the driest places on Earth (because all moisture freezes out of the air), so moisture is constantly being sucked out of your body through your pores. To replace that, you need to drink a lot of water.
To help ease the transition to this high-altitude, the medical staff offers 3 days of Diamox which (I believe) helps to offset the acidity caused by excess CO2 by forcing your body to pee more (which somehow makes your body more basic ... I *think* that's the science behind it. To replace that peed-out fluid, you need to drink a lot of water.
We're supposed to drink around 4 liters of fluid a day. This means a LOT of trips to the bathroom!