As bad as it is to use ancedotal evidence in this discussion I think it is as relevant as the findings of studying those that have died from water overdose. I once had heat stroke due to mostly dehydration and it was not even a hot day nor was I exercising even moderatly. Both the exercise part and the ambient temps when compared to normal days. It resulted in numerous bags via IV at a clinic only to be released and then promptly puking my guts out in their parking lot before they had LOML transport me to the hospital for an overnight stay. I suffered side effects from that that were severe enough that I could not work for a month. Face the facts, both dehydration and hypoatremia are dangerous.

Now years later I do not have heat issues even during hard exercise because I hydrate. I also supplement electrolites. I also acclimate to rising temps. I drink lots of water on a daily basis year round, perhaps my system has grown accostomed to it. 16-20 ounces an hour while out riding my bike with occasional bottles of gatorade or some other brand; I'm now trying to switch to Nuun. There is wisdom in being aware of the real possibilities of both too little and too much water. For what it is worth I ran by best mile time on a hot day in May with no wind, too long ago to remember anyting about humidity.......Bottom line is that there is much more to the story than just one part.