On real hot days, we used to run along the Connecticut River where there are some water fountains you can stop at and get a quick drink. I prefer to carry my own water though. There are some insulated bottles that will help keep your water somewhat cool. But even if you don't have one, warm water is better than nothing. So before you head out for a run on a particularly hot and humid day, make sure to take some water or some other water/liquid mix with you. Also, there are all kinds of bottle carrier belts that you can buy so that you don't have to carry your bottle in your hand. Find one that works for you and practice using it. You won't regret it.
One other thing to keep in mind on hot, humid running days. Don't be afraid to slow down or to run a little less distance. These types of conditions are obviously not ideal. But with some practice, you just might find that you are able to run much better in these conditions in races than many of the other runners.