Well, yeah, schedules. But more commonly it was said, "if you're not pissing, and pissing clear, you're not drinking enough." That was simple and crude enough for grunts to understand.
Since all the water we had, we had to carry, excessive hydration wasn't really a problem.
Nor is it for most modern people. I don't recall people collapsing in the street from hyperthermia twenty years ago before people started carrying drink bottles everywhere.
Every meal, have a drink to wash your meal down with. That cup of water/juice/milk/whatever, plus the water in the food itself, that's going to be plenty for you, unless you're doing hours of cardio in the heat.