I was listening to a lecture about music history the other day, during which the speaker went on a brief digression about the unexpected contingencies of history. As an example, he brought up the Minoan town of Akrotiri buried by the eruption of Thera some time around 1600 BC.
The explosion of Thera, and its impact on Minoan civilization, is often theorized as a source for the legend of Atlantis, which gives it a certain aura of magic and possibility. Add to that the fact that excavations of Akrotiri have found drainage systems and indoor plumbing, in this apparently very successful Bronze Age city, and you get a lot of speculation about What Might Have Happened had the volcano not buried the town and set the Minoans back a bit in their civilization. (How much the volcano itself was actually the cause of the eclipse of Minoan civilization on Crete and the rise of Mycenaean civilization on mainland Greece is one of those things that is hard to know but easy to tell stories about.)
This digression, unrelated to the substance of the lecture, reminded me of the odd hold which bathroom technology and practice seems to have on our ideas of how "advanced" a civilization is. Here was the lecturer jokingly speculating that if it hadn't been for the eruption of Thera, the Romans might have had wide screen TVs and fusion reactors -- yet although indoor plumbing is something which we associate with modernity because you only have to go back a century or two to get to a point where most of our ancestors didn't have it, there's nothing inherently "high tech" about indoor plumbing, especially on a small scale. Sure, setting up an entire city (especially one not built on a water way) with indoor plumbing takes a lot of work, but the sort of system which Akrotiri had certainly doesn't put it out of the reach of other bronze age civilizations. I don't deny that indoor plumbing is a very nice thing, but which constructing a ceramic plumbing system is very clever, it doesn't suggest that a civilization which hasn't yet figured out how to refine iron ore is on the verge of developing computer technology.
Similarly, when comparing Western Europe (particularly in the Middle Ages or early modern periods) with non-Western civilizations such as the Arab states or China, one of the standard things for pop histories to bring up is the reputed frequency of bathing in Europe versus other places. I am, of course, in favor of frequent bathing, as I have to remind my children from time to time, but again: the frequency of bathing is not necessary a good measure of how "advanced" a civilization is in its science, its literature, its political institutions, or its culture. It's simply an indicator of how much that culture values bathing.
I wonder if, perhaps, this all stems from the transitional period during which some classes of American and European society had modern bathroom technology (and the hygiene practices that go with it) while others didn't. If at that point society came to identify plumbing, bathing and flush toilets with being an advanced and modern person, this would have helped read back into history the "smelly old middle ages" and the general assumption that bathroom technology was an indicator for overall development.