As long as you listen to your body and hydrate when thirsty, a lot of our water requirements are satisfied with our food intake and our body is quite good at regulating water and electrolyte levels.
See https://www.mcgill.ca/oss/article/health-nutrition/water-myt...
Alternatively, I found a study that concludes that “consuming less than the 24-h water adequate intake may influence the risk of dysfunctional metabolism and chronic diseases” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6315424/
The study does state that the “adequate intake” is different for everyone, but at the end of the day you need to drink water. Spreading the idea that you don’t need to drink water is foolish.
I have often woken up in the middle of the night dehydrated and felt horrible-- half a bottle/glass of water later and I'm usually able to sleep through at least one more full REM cycle.
I think many of us could do with drinking more water each day, especially if exercising. But drinking water won't solve all of your problems.
Are you aware that some people don't ever feel the need to drink or feel thirsty? I myself used to barely drink water throughout the day and I have relatives who don't even drink a glass of water a day. I also have family who have specifically been told by their doctors to drink more water.
I never said water drinking is a panacea, I said most people would benefit from drinking a lot more.
To explain the latter: when you combine a carbohydrate with oxygen, you mostly get CO2 and H2O.
(No opinion implied on whether humans should drink more water.)