Some bodyworkers, e.g. those focussing on CSF rhythm and pelvic floor stability, say the coccyx has important function, though in most people it's stuck in place, slowly causing problems. Pottenger Foundation documented malnutrition over generations causing jaws to shrink, thus wisdom teeth needing to be removed in some.

I have taught about this topic for 20 years now postdoc to physicians in a board-certifying sequence in nutrition. I still find the issue confusing, as do my students, as I present conflicting opinions and studies to them.

One part that seems consistent is that, unless one has special needs, e.g. sweating a lot in athletics, e.g. susceptible to kidney stones, the average person does not seem to overtly suffer from what some would deem as dehydration. For example, the average person does not overtly suffer from waiting until they are thirsty, despite the lag between physiological dehydration and the mind getting past survival programming (the body often doesn't warn us of minor things, I assume so we can "get on with it" in a possibly scary world) and otherwise the mind allowing for the thirst to be noticed and acted on.

The piece encouraging large-ish imbibing of water/fluids that I haven't seen any research denying is bioimpedance analysis (BIA). None of the physicians, scientists, etc that I've read thus far (please educate me if you know different), saying "no, you don't need that much water", take on the BIA research/findings. Some of them I've been able to confront directly and everyone said they didn't know enough about BIA to discuss it.

Make BIA equal the electrical readings of the body's tissues (e.g. electrodes put at hand and at foot on one side of the body) that get plugged into (computer software) equations to give phase angle (correlated to membrane health, and supposedly vitality, though I find that a vague concept), lean vs fat body mass percents, hydration overall, and extracellular vs intracellular water percents (e.g. as one indicator of inflammation, e.g. as part of some hormone balance analyses).

I patiently watched BIA be used, watched the research and more in-the-field clinical literature accumulate, saw the hundreds of clients we treated in an AIDS clinic be analyzed with it with subsequent good interventions, etc, over years. I finally had to admit that it was a more valuable tool than just getting people to lose their excess fat mass -- it seemed quite valuable for above mentioned membranes, inflammation, and hydration.

At that point, I surveyed clinicians who had been using it for years and asked them what amount of fluids, especially water (since sometimes highly-sugared and/or highly-caffeinated fluids seemed to make them BIA "dehydrated"), seemed necessary to hydrate folks, to make their BIA say "hydrated". The answer consistently was approximately "divide your body weight in pounds by 2 and that is how many ounces of fluid to drink a day as a good first guess".

I don't want to believe it. E.g. so many clients find it too difficult to achieve that amount of fluid intake, even taking into account fluids in their food. However, again and again, I see the BIA show dehydration unless they are close to that amount of fluid intake.

And when one is dehydrated, the rest of the BIA is not as accurate -- the dehydration throws off the, e.g., fat vs lean reading.

So, either the many years of research and clinical work came up with wrong equations for the BIAs "cells and fluids" readings/analyses, i.e. BIA is saying people are dehydrated when they really aren't, or indeed many people have to do more than 64 ounces of fluid a day.

Perhaps too much beyond the level of these comments but I'll say it anyway: 24-hour urinary and spot salivary checks of adrenal cortex function in most clients I see suggest that hydration issues are secondary to adrenal function issues -- people wouldn't have so much trouble staying hydrated if adrenal function were better. Barnes Foundation and Brownstein knowledgeable physicians would claim that many people are also functionally low thyroid, which also contributes to dryness of skins. Omega-3 fats touters would also say many people are deficient in EPA+DHA and that also contributes to dryness of skins. So skin dryness (and maybe, thus, also poor handling of hydration by membranes in general) is not a sole indicator of hydration.