8 x 8

You've got it right, Brian. I believe there is consensus medically that not enough water is not good for a healthy body. The function of the kidneys is to filter out waste products from the blood and promptly dispose of them through elimination (urination). If inadequate water is consumed, the urine concentrates and kidney function is impaired. Concentrated urine directly leads to kidney stones.

Just consider what folks on dialysis are doing and why. Their kidneys are not functioning properly, so the blood must be cleansed externally.

And, death is the prompt result of failure to ingest water (or fluids) - in just a few days (whereas starvation from lack of food for energy takes a substantial period).

Now, I suspect I don't drink enough water either, but the standard should not be if you are thirsty or not - some people don't respond to thirst signals for various reasons relating to body chemistry. Concentrated urine (dark in color) is the signal which should not be ignored.

So is 8 glasses daily enough or too much? We may never know that given the difficulty of conducting research on humans over an extended period of time. But the general advice to drink lots of fluids can hardly be considered unscientific. In this case, debunking the myth creates another kind of moral/physical hazard for those who think the evidence says it doesn't matter. It does matter.