OK, "drink before you're thirsty".
Yeah, as I noted in Fueling, not only is the water "hydrating" it is also transporting fuel. The fuel management part of it might be enough, but, how to tell?
Most of my bad examples have been me! It is really hard to tell if dehydration or over-hydration with no electrolytes, is a problem until a person, figuratively, keels over.
Definitely, drink before thirsty, but when and how much to avoid !!FAIL!! cramps, slosh, desiccate, roast, etc.?
Yep, sure fired way to !!FAIL!! and end up road kill is to not worry about hydration and electrolytes!