The mishnah discussed on this daf includes a definition of what items may be used for an eruv hatzerot, as well as what can be purchased for your maaser sheni money in Jerusalem. The opinion of the mishnah is that all foods are fine, except water and salt, presumably because they are not considered food.
However, Rabbi Eliezer and Rabbi Yosi ben Hanina hold a slightly different opinion. They suggest that while water OR salt may not be used, saltwater is permissible, since it is like a food. The question is, did the shops on the main drag in Second Temple Jerusalem sell ready-made saltwater, as they do today in certain American supermarkets?
Thanks to Tamara Spitz for the idea.