Think about all the ways water factors into The Fall. The woman whom Jean-Baptiste fails to save dies by drowning. Jean-Baptiste has chosen to live in Amsterdam, a foggy city of canals, and a "soggy hell," a "negative landscape." The place is full of bridges over water that he’s too afraid to cross at night. The laughter Jean-Baptiste hears comes from the water. He prefers to live on islands, surrounded by water. He delivers one of his monologues to you while on a boat. He is on an ocean liner when he sees a black speck in the water and realizes he can never escape his shame. Speaking of that ocean liner, check out this passage:
Then I realized, calmly as you resign yourself to an idea the truth of which you have long known, that that cry which had sounded over the Seine behind me years before had never ceased, carried by the river to the waters of the Channel, to travel throughout the world, across the limitless expanse of the ocean, and that it had waited for me there until the day I had encountered it. I realized likewise that it would continue to await me on seas and rivers, everywhere, in short, where lies the bitter water of my baptism.
Baptism! Remember, Jean-Baptiste is a skewed parallel to John the Baptist. But instead of using water to cleanse someone of sin, Jean-Baptiste’s sins lie in water. (Maybe that’s why the water is so bitter.) Now look at the next line: "Here, too, by the way, aren’t we on the water? On this flat, monotonous, interminable water whose limits are indistinguishable from those of the land?" Jean-Baptiste can never escape water, just as he can never escape from his crimes (the dead woman in particular, but his hypocrisy in general). By coming to Amsterdam, then, the city of canals, fog, bridges, and rain, Jean-Baptiste has "reversed the reasoning" yet again. Rather than run from his guilt, he has run towards it. He has manufactured an escape that requires Copernican logic.