Plumbing mysteries of misters
"Can you explain why a misting system can cool a patio up to 20 degrees, but when the atmosphere has its own moisture - high humidity - it doesn't have that effect, and in fact it feels hotter instead of cooler?"
Good succinct answer. Note that it says "evaporate immediately", which isn't the case in a lot of cheap systems around Phoenix. You know the ones, you step by them and are promptly soaked to the skin. Amazing, we're in a drought and we're spraying drinking water into the air...