title_body: Can a brewery in California fill any growler?
upvoted_answer: They can, provided that they:
  
  
  Cover up existing labels
  Add their own label containing the brewery name, beer name, and abv.
  Are a brewery (bars and retailers cannot).
  
  
  You're not alone in being confused, though.  A lot of breweries didn't really know either, and as a result decided not to, just to be safe.
  
  Further complicating the issue is that many breweries just don't want to, either because they make money on their growlers or because it's a pain to deal with the labeling when their bar is busy.
  
  SFGate has a decent article for further reading.