Actually, it's not necessary to keep your urine crystal clear. The color will vary with the volume of urine. You could be normally hydrated and still have colored urine if the volume is not that large. Sure, if you drink more water than your body actually needs, urine volume goes way up and your urine will appear clear, but in that case, you're wasting precious water. That's fine in every day life, and probably a healthy habit, but a waste when water is scarce. Oh, and of course, diuretics can increase urine volume, resulting in clear urine, but it's actually dehydrating you. Actually, I find that very cold weather also acts as a diuretic for me (it's called thermal diuresis) which can result in clear urine even though I'm not drinking any extra fluids.

The opposite would be a more accurate indicator. If the color is dark, then I would think about drinking more, although that still isn't necessarily dehydration. And various medications can cause dark urine regardless of hydration state, so that's something to be aware of.

Personally, I think the best indicators would be to gauge how you feel and also to weigh yourself. If you're losing weight during the day, then you're becoming dehydrated, particularly if you're experiencing the typical symptoms like headaches and cramping. Of course, high temperatures, low humidity, heavy exertion and other factors may require you to drink more to stay ahead of the dedration curve, so to speak, but for normal folk, weighing yourself will work. Actually, I'm curious if those members who are drinking like a couple gallons per day, if they are consistently gaining weight over the course of each day versus their morning weight. If not, then that's quite a high water requirement that surprises me, for non-athletes.

That said, I'm glad you mentioned the danger of too MUCH water. More of an issue for athletes, generally, but an important point. I made a long post about that a while ago, if anyone's interested in reading more on that topic and how "common wisdom" has changed over the years.