Yup...its not the lack of water that gets you.....it's the heat and sun exposure. There's a body temperature point where all the water in the world won't help you. Your body just won't process it. The biggest hiking lessons I've learned in the last 15 years is "white floppy dress shirt", "big hat", and "hike with an umbrella". You can hike in complete comfort out on the desert floor, if you are in perpetual shade.