This happened to me a few years back, in a regular bakery. I asked for a challah, took it home, and it was tasteless, so I didn't return to that bakery. A year later, I'm surprised to taste a delicious challah as a Shabbos guest, and when I ask where they got it, it was the same bakery. I hadn't realized there were now two kinds of challah. I assumed the reason they gave me the water challah was not due to its popularity, but because it had fewer expensive ingredients (egg, sugar).