Its not against it, its just not conclusive everyone needs the same amount or it has the same benefits across the board.

I'll add one too since its on topic with reply;

Caffeine drinks like coffee will dehydrate you. Its a diuretic but you consume more water through it then you release. https://www.mayoclinic.org/healthy-lifestyle/nutrition-and-h....

Don't hold me to this, but if I recall, the recommendation is to consume 8 cups (1 cup = 8 oz ≈ 0.23L) of water a day, and the water contained in our food counts. This is to say, people conflated 8 cups of water to mean 8 glasses of water.