i used to know if u drink water during the stand up and shout greeting and teacher name is wrong

or

during teacher is teaching, and u drink water then it is wrong

these were my time

i can only drink water when teacher is marking the paper / or give freedom self study / or some teacher simply dont care

most of the teacher who tell u cannot drink water blah blah blah blah is ppl dont like getting their attention get disturbed by some drinking water student.