The weather has really warmed up this week. I ran with my daughter yesterday when it was 80 deg with sunny skies. We stopped half way through our run to get a drink at the local golf course. On the way home my daughter started to slow down and had to walk on the way home. Even the most fit people can still be slowed to a walk when their hydration is inadequate.
On days that I run I always make sure to drink water through out the day. And one hour before I run I make sure to drink a bottle of sports drink. And just before I leave I will drink another 20oz bottle of sports drink.
If the run will last more than a hour I will plan stops along the route to drink more fluids. I think that sports drinks are a lot better than plain water because, of the electrolytes.
Water contains zero electrolytes and the body will use what is available as you sweat. Almost every time that I have suffered badly on a hot day was because my electrolytes have become depleted.