The military abides by the heat index... They aren't idiots, either. BTW, they also are a lot better at pushing water. Unless you have kids under your nose all the time, you cannot regulate water intake.
There aren't supposed to be consecutive, fully padded practices in 2-a-days, are there?
I would say do 1 morning practice with a focus on indy period and maybe special teams install, then an evening focus on team stuff.