What's better than plain old water? Electrolyte water, that's what.
I started drinking electrolyte water (you know, Smartwater, or one of its generic cousins). Despite looking at the nutrition label and ingredient list, I still am not sure what electrolyte water has in it. Apparently, the electrolytes are just for taste. I wasn't sure the electrolytes were doing anything. But I kept drinking it during long runs because it wasn't hurting. The tap water in my area is nasty, sometimes even after it has been filtered. While expensive, electrolyte water tasted better. Much better.
Over time, I noticed there WAS a difference between plain water and electrolyte water. It didn't make a difference in everyday runs, say your average easy pace shortish weekday run. But it did for hard or long runs, say a longish pace run. A few weeks ago, I did an 8 mile pace run on a treadmill. I thought I would be OK with my regular water bottle filled with filtered tap water. I started to feel nauseous a few miles from the end. This has happened a few other times too. It definitely happened on a 12 mile run in Washington, DC on a humid and warm day when my bottles were filled with tap water. Of course, this could have been lack of electrolytes in general on those runs, but I think part of it was no electrolyte water.