UPDATE: A comment below from "Tony" said this:
Obi-Wan was originally supposed to be smoking his hookah, but the scene was changed during filming.
I found this description in the revised 4th draft of the Star Wars script, as of April 19, 1976. Just after Ben and Luke watch Artoo's message from Princess Leia in Ben's hovel...
"There is a little static and the transmission is cut short. Old Ben leans back and scratches his head. He silently puffs on a tarnished chrome water pipe. Luke has stars in his eyes."
Rob - The Bearded Trio