ive done this a buncha times... at first not to pick up but more for the actual reason i say it lol... but now it works as a good open.....

while shes placing her order.. or about to......
go up beside her and say

"hey.. order me a glass of water pls... ull get it before i will here....its crazy busy."

they ALWAYS do it for ya....

while ur waiting say "wow i love ur boots.. did u come on horseback?"

sometimes they'll say "aww...poor baby cant afford a real drink?"

pounce on that

i dont drink much when clubbing so i really do drink water and have found askin pretty girls to order water for u gets it a hell of a lot faster than trying to get it urself....

Too much investment with the wording man ...
OF course the body languege is all important but the plz!
"hey grab me a water, no ice and a slice of lemon!"
Be pwoerful and show grace, because when she comes back with anything

"what, its just a water, it costs nothing silly!"

Act asif it happens all the time and she is just acting silly