Steel, don't understand the opposition to drinking water on the line....I can understand not eating on the line, or drinking soda, tea, coffee, etc (might mess with your palette) but water? Especially if it is in a proper, lidded cup so it can't spill or contaminate the line. What is the issue?
I think proper hydration is essential to maintaining health...is it not? No offense, but that business about not drinking water to keep yourself from sweating is nonsense. If your body is purposefully shutting down your sweating mechanism then then that means you are dehydrated (your body is holding on to fluids for dear life).
This sounds like...no offense, again....an outdated viewpoint. To me, not being allowed to drink water on the line would be comparable to your examples of "19th century" thinking. I can tell you, but a little cup of water every 30 minutes is not going to keep me hydrated, especially during service. There are times when I don't drink enough water (before and/or during service) and I start to feel sluggish and get a bad headache. Then I know I am getting pretty dehydrated.