Apparently I was victim to a widely circulated myth. Apparently though, that board also specified that most of that recommendation was covered by water within food. The "IT HAS TO BE ACTUAL PURE WATER" thing was added on later by others.

So where did the myth of the 8 glasses come from? Fox says it likely stems from a decree from the U.S. Food and Nutrition Board issued back in the 1940s. It suggested that everyone drink 2.5 liters (84.5 ounces) per day — so not far off from today's standard. But even back then, that same recommendation clarified that a majority of that water comes, not from a glass, but from "prepared foods."

Source: https://www.tuftsmedicine.org/about-us/news/medical-myths-drink-8-glasses-water-each-day