I don't know how this word came to be classed as common, but there's no danger of it coming up in a 9-letter puzzle. Not every "common" word is available as the seed word of a 9-letter puzzle, and that applies to jerkwater. Of course it could come up in a 10-letter puzzle if there's a 10-letter word using these letters, but I doubt it.
There could be quite a few surprises awaiting us in the 7-by-many puzzles, in the form of words that might be badly labeled but have never shown themselves in any puzzles before.