Hydrate, or Be Dehydrated

Hydration is essential during every season, not just during warmer weather. Urine You're in for a shock if your pee is brownish/not yellowy whether sitting or playing Ultimate. Lack of fluids may cause less than optimal performance on the Ultimate field.

The Boy Scouts - who offer a belt loop for playing Ultimate - chart out pee color & de/hydration:

There's no need to try to super-hydrate pre-exercise; your body can absorb just so much fluid. If you overdrink, you then may have to (inconveniently) urinate during exercise; the kidneys can only make about one quart of urine per hour. A wise tactic is to tank-up two or more hours pre-exercise; this allows time for your kidneys to process and eliminate the excess. Then drink again five to 15 minutes pre-exercise.
[SOURCE: Active.com]