My understanding of the current best advice is to pretty much drink water at a reasonable rate while you have it, and that rationing at a level clearly below metabolic needs proffers no real physiological benefit. Still, it seems that many people in survival situations without water supply eventually get down to the thimble-full rationing level, anyway.

I once found that my water bag had leaked dry "out there." I was in absolutely no actual danger at all, and knew it. It was just an ordinary dry, hot day on a dusty trail, but not extreme heat or humidity, and I only had to hike about five miles over a ridge to reach certain abundant water, or turn back about four miles, or I could have grounded my heavy pack and come back for it once reloaded with water (I was loaded for an eight day backpack trip). Still, I found the experience very disconcerting. To this day, I still carry "too much" water, and hold an inviolate spare 1/2 qt in a separate container always.

Jeff