The Waters shot should be one where Stevesie pours it, slides it down the bar, and another patron grabs it before it reaches you and drinks it.
Or one guy buys it for his friend, but as he is getting ready to hand it to him, a random guy in the bar slaps it on to the ground.

Or you make the waters shot and then you make a clearly superior shot and the patron has to drink the waters shot while the bartender places the better shot on a shelf behind the bar for the patron to look at but not have.