Running in the Heat:
I myself enjoy running in the heat, I don't quite know exactly why, but I enjoy it. I'd rather it be 90 degrees out than 32 degrees. I think it is mostly because I can handle the heat fairly well, or at least more than some. I seem to be able to quite hydrated well in hot or cold conditions, but this often leads to slight over hydration under "ideal" conditions.
Well, enough about me, here is the quick tip for running in the summer heat, obviously you need to stay hydrated but you also need to replenish your electrolytes. More or less if you are out there working up a good sweat you need sodium along with water to stay hydrated.
You can do this by drinking sports drinks like Gatorade and Powerade, but if you look at the ingredients on them they are mostly Water, Fructose and sodium. i.e. Water, sugar and salt.
Water is even better is coconut water which actually is the best source for rehydrating your body, though it is a bit more that Gatorade.
I actually like to drink either coconut water or make a really watered down fruit smoothie and add about a 1/2 teaspoon of sea salt. You are getting the same water, sugar and sodium as you get in sports drinks but it is a little more of a healthier alternative.
Here is another good article from Runner's World on running in the summer heat. Heat-Tested