Venetians and Venetophiles often wax nostalgic about the days when central Venice had more than 150,000 residents. (Since World War II, the centro storico's population has dropped to about 58,000.) They conveniently forget how many of those old-time Venetians lived in overcrowded apartments without modern conveniences.
In the photo above, you can see the entrance to municipal showers in the city center where poorer Venetians once went to bathe. Today, the showers are gone, having been replaced by public toilets.
The toilets are expensive--1,50 euros for tourists, less for locals--so it shouldn't be surprising that some visitors and residents whiz directly into canals. (And why not, you may ask, since most of Venice's raw sewage is flushed into the canals anyway?) This is not a good idea, especially if you've been drinking, since tipsy tinklers have been known to slip, fall into canals, and drown. We once saw a body floating in a canal near our apartment in San Polo the morning after Martedi Grasso, or "Fat Tuesday," when boozing and canalside urination are rampant.