Dehydrated Water…almost

I don't think you're missing anything. Most likely that hiker was drinking more water than necessary because his lack of electrolytes was being felt as thirst. You still need water to make energy, and electrolytes cannot substitute. Of course, water requirements do vary from one person to the next.

I ride bikes with a guy who drinks pedialyte in lieu of water. It was popular with triathletes awhile back which is his background. On any given ride we bring the same number of bottles, of course as Douglas points out our requirements could be different, he doesn't drink less … and I supplement minerals/electrolytes. It is amazing he can gag down the stuff pushing hard cycling. There was a famous female climber who drank cherry kool-aid because it made drinking palatable and she would keep hydrated. Very few of us are going to get hyponatremia from drinking too much plain water but if you see the telltale white stains on your clothing it's time to up the electrolytes particularily sodium.
Does anyone know if the old saw about drinking enough that your urine is clear is based in fact?

I think Pedialyte is nasty tasting, at least the stuff I gave my kids (they didn’t seem to mind).

My solution (pun) is ElectroMIX from Alacer Corp, the maker of Emergen-C. One lightweight packet (0.17oz/5g) makes one liter of electrolyte solution, as in a typical sports drink but without the sugar. I get plenty of carbs in my snacks so I don’t really need to carry the sugar component of sports drink. ElectroMIX has a faint lime flavor (not zesty) and no artificial sweetener.

This topic was also discussed in this BPL thread.