Well when I'm a co-instructor there is plenty of times where I can sip water, as I will not always be right in front of the kids, to the water in take is not so bad.
It is when I'm the leading instructor I'm right in front of the kids and because I'm the one talking I need to drink. And when they see me drinking something they want to drink too even though they do not need it. And when 7 kids are "playing" around with water bottles, even when you tell them to be quick you will have lost 5min of the teaching time.
I have started to just drink and ignore their request for a drink, but give them some water between each drill, some of the kids are ok with it when you tell them that they will get some later.