Even though the gym has AC, you're gonna sweat. Stay hydrated for your health! It doesn't have to be plain water, any non-alcoholic beverage helps. Sip on water throughout the day, and consider electrolytes. Ask if you have any questions on that!
And really, it's a myth that coffee is dehydrating. Caffeine can make you go to the bathroom sooner than later, but there's still more water in coffee than the caffeine would make you pee out. So enjoy that iced coffee 😏