Yes. I read an article some years ago exposing the "lack of hydration" scam. Like people have to be reminded to drink water when they're thirsty. There's about a zero chance that appreciable numbers of people in this country are not being properly hydrated.
Some people think it was a scam generated by all the businesses that have popped up in the last thirty years selling bottled water.
Yes, the "8 glasses a day" is a myth. In fact, if you eat a reasonable amount of vegetables you theoretically don't have to drink any water, and still be plenty hydrated.
Your colon if it's working properly can and WILL absorb a LOT of water, which you then urinate out.
Your body likes to be at a certain osmolality, and too much water dilutes that.
Too little water, and your thirst center is triggered.
The body is a pretty clever mechanism.