"The very first year I taught, I realized how much time I was wasting in my classroom for my students to be constantly raising their hands," said Fran Nadel, 25, a second-grade teacher at Woodburn School for the Fine and Communicative Arts in Falls Church, Va. "I realized if they could do this without talking, I could send them somewhere with a flick of my finger."
"On a recent morning, Nadel huddled with a reading group of four students while the rest of her students worked independently at their seats. Every so often, a hand would shoot up from the back of the room. Nadel would respond almost imperceptibly, and the reading lesson would continue uninterrupted as the student scampered off to the bathroom, pencil sharpener ("S" for supplies) or the trash can (the letter "T")."
Of course, each teacher has to set out, at the beginning, rules about getting water, etc. But especially for elementary students, it seems like a good thing to try (plus they might get interested enough to learn sign language).
I recall using something non-verbal like this with my sons when they were little. If I was reading or doing something with one and the other one was clamoring for my attention, I'd touch his hand or forearm and give it a squeeze which meant, "I know you are here and I'll be with you in a minute." It seemed to acknowledge their presence without interrupting what I was already doing.