I've always thought that my body should be able to tell me when it needs more water and I shouldn't need to force down extra water.
Make it easy to drink automatically. Your body knows when it feels like having a sip, if that doesn't involve breaking your mental flow, you will have the sip. Simple as that.
There's a world of difference between being dehydrated and a bit thirsty. Try going to the beach for a day and forgetting to bring any water. You'll know the difference in a few hours.
The fun part is that you'll feel tired all day and all of next day too. I've done this way too often in various combinations (roadtrips, plane flights, marathon runs, surfing and forgetting to bring water, etc.)
A couple guys went into coma in a nearby Buddhist temple a few years ago. A dozen friends planned a "body cleaning weekend" where they fasted and drank lots of water. They got a water overdose, a condition known as hiponatremia[2] (literally "low sodium" in the blood plasma). This condition is pretty nasty, because it messes with osmosis.
So kids, drink your water but eat a little salt as well.
[1] http://www.brainyquote.com/quotes/authors/p/paracelsus.html [2] https://en.wikipedia.org/wiki/Hyponatremia