While it is OK to use water as a stop for film and RC papers it is not good to use it with FB papers. If an acetic acid stop causes problems then use and odorless citric acid stop bath. A 2% solution of citric acid will work. When usng water you should replace the water a few times to remove as much developer as possible before the fixer.
And why is that?
I've been using water only for a few years.