I'm sure this has been done before so apologies.
My DD (7) has just had a new teacher who changed the routines around a bit. They are now only allowed to drink water at lunch and are not allowed to quickly grab their bottles whilst going down / coming back up from break time or assembly. This is apparently done so they won't have to go to the toilet too often (which is just outside their door).
I think its a bit out of order but before I have a word I wanted to check whether IABU. I know its important to stay hydrated and I don't think this is achieved by drinking before school start and only then drinking again some 3 hours later.