Many have wondered about such a thing to see it in the movie. Well, apparently it's a very widespread superstition in Sweden. I reproduce here the complete text of an article that I found on the internet about superstitions in the world. The part referring to clear Sweden:
"Some Swedish manhole covers have the letter K of" Källvatten "(drinking water), but many think it is to represent the word" Kärlek "(love); and other sewers have the letter A of "Avloppsvatten" (wastewater), which many others interpret as a symbol for "Avbruten" (rupture). In Sweden it is easy to recognize the locals when they see them jumping to avoid stepping on the latter ... and they say that the "antidote" to reverse bad luck in the love of the person who accidentally steps on an A is to give him three pats on the back."
Elin's shoes over a sewer, in the movie.
Written in Spanish by Mordecai in this forum (viewtopic.php?f=11&t=1880), translated to English now.