Some schools don’t allow children to leave the classroom to get a drink of water unless it’s at recess or between classes. So that’s why they carry water bottles nowadays.
Progress! When I was in school we weren't allowed to leave class OR have a water bottle. If you had food... good luck, that was like the worst school crime for some reason.
Though I don’t remember not being allowed to drink something between class breaks ever being a problem growing up. Classes aren’t that long.
The other thing is that we mostly only had glass bottles back then, so of course kids wouldn’t carry those around.