That is actually not unscientific... it is true. One of the credos we use at Burning Man (where hydration is SUPER important) is "piss clear." The darker your urine is, the closer you are to dehydration. Of course, there are some foods/vitamins that will make urine more orange/darker but it's generally a good guideline to use.
I am a bad person to ask about this because my water bottle is like my pacifier. I walk around with it all day and if I don't have water nearby, I get a little panicky.
If I'm doing long runs, I'm careful about hydration but if the workout is under an hour, I go by thirst.
I have also heard that somewhere around 90% of headaches are due to dehydration.
I'm curious about that 90%.
if i only drank when i was thirsty i'd be dehydrated, and headachey, all the time. as it is, i'm dehydrated a lot of the time.
when i think of olden times, i think of people going to the well and guzzling like 3 cups of water at once. if we did that a couple of times a day we wouldn't need to carry water bottles around sipping. i think the water bottle phenomenon is for people who don't like to have to wait to get to the well and would rather sip constantly. whereas i'm not a sipper so what i need to do is be a well-gulper, but with all the modern distractions it's easy to forget.
i think we are agreeing because i agree we can know our own bodies and just be able to know how much water we need. i just think that, at least for some people, it's not going to be solely based on thirst. we'll still know how much we need but it just might be through different senses.