Every campo has one or more. The wellheads that were essential in providing fresh water to the residents of a city surrounded by salinity. They’re all capped and padlocked.
The reason is that as the fresh water was extracted from the strata below the city, it left a void that the sea seeped into and that salt water is another factor in damage to the city’s foundations. No more water from the wells then.
All those tourist have to drink, and the bottled water they consume creates further issues in waste disposal, so a few years ago everyone arriving in the city was given an empty bottle and a map of the 122 public fountains. An interesting approach in a city whose place in literature is notorious for an outbreak of cholera*; to prove its safety the bottles were labelled with a chemical analysis of the fountain water!
*Death in Venice – Thomas Mann