The free tap water that is dispensed from the beverage gun located behind a bar.
First recorded use: New Orleans, December 2011.
Dude: Can i get two gun waters.
Loser Bartender: Two what?
Dude: Gun waters, you know, the water that comes out of that gun.
Loser Bartender: Sorry, all we have are these $8 bottled waters.
Dude: That's bullshit.