When one takes the pitcher out of the fridge and drinks the water out of the pitcher. Usually a younger brother.
Guy#1: Dude do you know who's the fucking water bender?
Guy#2: Yeah, I think it's Guy#3, I saw him drinking out of the pitcher this morning.
Guy#3: Sup? Who's been bending the water today?
A Waterbender is a person in the TV series Avatar: The Last Airbender who is able to manipulate water. Generally used for fighting, it can also be used for healing. Waterbenders have the ability to control the temperature of water as well, creating ice and steam at will.
Waterbenders deal with the flow of energy; they let their defense become their offense, turning their opponents' own forces against them. The technique of redirecting Lightning, which is a Firebending attack, is based off of this fundamental Waterbending concept.
Katara, a main character of Avatar: The Last Airbender, is a Waterbender.