I think it’s diet. I stopped eating shit and do not need or want water until around dinner time typically. I am not dehydrated at any point, urine is completely normal and not dark at all. I have a morning latte and noon coffee (8 ozs each) and feel no thirst until around 3-5 pm. Usually up at 7 am. It’s one of the many interesting changes I’ve noticed since changing my diet.

Yes and no fat, soil magnesium depletion and mass marketing against tap water

Look into salting your water and also Sport Drink. I used to be guzzling water, but once I dialed in my electrolytes and minerals it reduced by 30-40%.

I think it's because since the late 20th century, people are overloaded on carbs (specifically fibrous ones). At no other time in our history have we been constantly told to eat fiber. Dietary fiber is not necessary for health. But if people do consume a lot of it, an abundance of water is needed to properly move it through the intestines.