Originally Posted by
nancy sv
If you have enough water, wetting your hat/shirt/whatever can help cool you down. When you're miles and miles from the next water source and are carrying gallons of water, you're better off using that water to drink rather than wet your clothing.
I would say the opposite for extreme heat. You can sweat a lot faster than you can absorb water, so if you are relying on only sweating to cool you down, you will dehydrate eventually. You will also need more electrolytes because you lose those too. It takes a fixed amount of energy to evaporate a given mass of water, whether it's sweat or just sprayed on. That means it drops your temperature either way. As long as you aren't spraying half of it onto the pavement, you will get the same cooling from spraying yourself down as you will from sweating buckets. Obviously your body is better at fine-regulating your temperature, but if it's 100 degrees outside, you are going to be dumping a lot of heat anyways.
In extreme dry heat, at every mile marker I would take a mouthful of water and spray a squirt on my front and thighs. Works out to about a liter every 15 miles or so.