To me, it’s a no brainer to take water on every run over an hour.  I always weigh myself before and after a run to see if I am maintaining proper hydration.  Sometimes I drop as much as 5 pounds on a run.  Many people mistake this for burning fat.  Don’t we all wish that!

I usually consume 1 liter per hour when the weather is moderate.  On hot days it’s double.  I have been using the Nathan dual 22 ounce bottle hydration fanny pack.  It usually will get me in between water stops.

Water is always more important than fuel on runs.  Given a choice, I will bring water over food.  I can run 8 hours without food.  If I tried running 8 hours without water, I would collapse from dehydration.