Many years ago, I taught English in Querétaro, which was then so small you could easily reach every part of it on foot. The first time I crossed the town early in the morning it was so quiet I expected to see nothing but empty streets. To my surprise, I found neither the streets nor the sidewalks empty. It was, in fact, downright dangerous to walk around at that hour, because, without warning, gallons of water (clean, fortunately) might come sailing out of any doorway at any time. This was my first introduction to a curious and charming Mexican custom which, for lack of a better name, I will call the Spotless Sidewalk Syndrome.