I'd like to get a look at that "pellet gun" that a 17 year-old man was holding to an officer's head. Is "pellet gun" another term for "bb gun?" If so, bb guns are often made for adults and made to look a hell of a lot like the real thing. Most water guns, on the other hand, are made for children, are child-sized, and would be nearly impossible to mistake for a real gun. Even when painted black.
A CO2 pellet gun held directly to a person's head is not a toy. It would be a potentially lethal weapon.