Everywhere we go we hear "Hydrate!" "Hydration is Critical!" This follows the government/military penchant to use a multi-syllable Latin-derived word to show that a given task must be done. "Drink!" would not work because it would lead to the smartass retort "Drink What?" then "Drink Beer!" So we hydrate. But not always.
Because when one hydrates, one will sooner rather than later need to un-hydrate. Which is more of a problem than you would think. If we listen to closely to the all the calls to hydrate then get on a bus, no one is going to stop the bus. The hydrated soldier might have a couple of hours of serious discomfort before being allowed the natural consequences of following his orders.
And since we travel in groups, we line up for everything. That means the poor soldier in the back of the bus does the un-hydration dance in a long lane waiting for one of six portajohns with lines of 50 at each one. Like every other health pronouncement, one size never fits all and some people hydrate to the point of pissing away necessary salts. So they end up full of water and with dehydration effects.
I would hydrate more if I knew I could take a leak when I needed to. But it is quite clear the opposite is true. If I hydrate I will be sitting in a bus or Humvee think that nothing could be more beautiful than a brown plastic Kamal Al-Sultan (the local contractor) Portajohn. So I drinking slowly and often, same as when I am racing, and pay attention for signs that I need more water. And since much of our hydration is by individual half-liter plastic bottles, I always make sure I keep at least one empty with me in case we are confined and my personal emergency becomes dire.