Well, I’ll tell you something I do which really works for me. I have longish hair, worn in a braid and pinned up with a clip.
I repeatedly go over to the hose, or a water tank, and completely drench my head. I turn it over upside down and let the hose run from my neck right off the top of my head. If a tank. I sink my whole head into it. I flip back up, lean back squeeze the extra water out, and continue on.
The trick is to keep the hose on it until your head has cooled off. You can tell by feeling with your fingers if its still hot against the scalp. Once its cooled off, you can come up for air, squeeze out, and the wet hair will keep you cool for another good hour, really.
If you are dunking in a tank, keep the top of your head under water until the heat coming off your head has cooled.
Feels reaaallllly good. Yum.