Water

In gay circles water refers to either GHB or GBL; in San Francisco, a lot of guys carry bottles of GHB or GBL premixed with another liquid, usually real water of the H2O variety, in their backpacks making it convenient to drink while on the dance floor, at a sex club or at a party without having to measure it out first.

Calling up a friend before going out. "hey will you bring some extra water with you tonight, I'm out"