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.

Kids aren’t allowed to go to the toilet in the middle of a class?

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.

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.

Leaving the classroom to pee was frowned upon during lessons, and during breaks obviously there was a queue.