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 Today, the showers are gone, having been replaced by public toilets.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.

ABOVE: Before cooling your heels in Venice's canals, put on latex socks.

In the summer months, it isn't uncommon to see tourists dipping their toes or feet into Venice's canals, presumably in an effort to keep cool.

Before emulating those clueless or intrepid visitors, consider this: An estimated 90 percent of Venice's human waste is flushed directly into the city's canals, and a public-health study detected Hepatitis A virus and enteroviruses in 78 percent of the canals that were tested over a two-year period from 2003 to 2005.

Venice's canal-based sewer system is more than a thousand years old, and it continues to work well by medieval or pre-Victorian standards.

The principle is simple: Venice's canals are flushed by tides twice a day, and the receding tides pull waste from the canals into the Venetian Lagoon and ultimately toward the Adriatic Sea. As a bonus, saltwater has a mild sanitizing effect. (Dilution helps, too--there's far water in a Venice canal than in a typical sewer pipe.)

Critics point out that detergents and other modern "grey water" pollutants interfere with the natural breakdown of fecal matter. That may be true, but even if it weren't, the fact remains that dumping raw sewage into public waterways isn't acceptable in the 21st Century.

The city has made some efforts on the sewerage front--renovated properties are theoretically required to have pozzi neri or septic tanks, for example--but for the most part, building drains flush directly into the canals, and the gospel song Wade in the Water is bad advice for visitors to Venice.

 More photos:

ABOVE: A visitor enjoys a fecal footbath. 

ABOVE: During acqua alta (tidal flooding), water from Venice's polluted canals oozes into the streets.

ABOVE: A pozzo nero ("black well") boat sucks out a septic tank at a bar near the Campo San Giacomo dall'Orio.

ABOVE: A sewage boat arrives to collect the contents of a septic tank or a "pozzo nero" (cesspool) in a Venice storefront.

Sewage isn't the most appealing travel topic, but if you're at all interested in urban infrastructure, you might as well learn where things go when you do.

Most of Venice's sewage goes directly into the city's canals. Flush a toilet, and someone crossing a bridge or cruising up a side canal by gondola may notice a small swoosh of water emerging from an opening in a brick wall. In theory, such waste is supposed to be purified by septic tanks, but such systems are the exception, not the rule. (Septic tanks are most common in restaurants, hotels, and other structures that have been gutted and renovated in recent years.)

From time to time, septic tanks need to be emptied by a pozzo nero ("black well") boat, which hauls the muck away. Buildings that use cesspools to store untreated waste also need an occasional pumping-out. In the photos and video on this page, you can see how the process works.

BELOW: A hose runs from the boat or barge to a temporary sewer pipe on shore.

BELOW: The sewer pipe runs across a square into a storefront where a pump draws sludge or waste from an underfloor storage tank.

BELOW: This video shows a sewage boat pumping waste and cruising away after sucking up a tankful of muck.

Want to learn more? Read Venipedia's illustrated article about sewage disposal in Venice.