In the summer heat, you don't need to do anything to dehydrate. It just happens, continuously, silently, monotonously. By the time you start to feel thirsty, you are already dehydrated. Thirst is your body’s emergency alarm bell ringing to tell you that you are already stiffening up in all the wrong places, feeling worse and thinking less clearly than you would if you were sipping water. Like 'becoming sat' after years of being trained to be sedentary, almost all of us have been dehydrated for so long that this feels normal to us. We have learned - we have been taught - bad habits.
The usual response to thirst is to upend a hot cup of coffee or a chilled can of energy drink into yourself and carry on because these things are tasty and life is short. These things are good for hydrating you, they just aren't as effective as water. Drinks that are particularly warm or cool tend to slip through as if not touching the sides, prompting more trips to the toilet. Drinks closer to body temperature are absorbed more easily and so hydrate you more effectively. While some secretive beverage tyrant seems to demand colder and colder bottled water, drinking water from the dispenser or from a bottle that’s not been stored in the fridge is best. Only alcohol actively dehydrates, which is why drinking even clear spirits tends to result in a dry mouth, headache, stiffness and hangover the following morning.