The Piazza Fountain is available as one of the options through the Piazza Selection Kit which also allows to upgrade the Piazza Fountain to level 2, thus improving its properties.
For more information see the Set Bonuses.
The Piazza Fountain comes with the special set bonus. When it is adjacent to other buildings belonging to the Piazza Set, it will receive special bonuses.
The Piazza Fountain can be upgraded by Piazza Fountain Upgrade Kit item. To upgrade the Piazza Fountain, use the Piazza Fountain Upgrade item on the Piazza Fountain that is already situated in your city. Its upgraded version will then be placed directly on the same spot in your city and the production timer will not be reset. Note that the upgraded building will be from your current era, even if the old one was from one of the earlier ages.
Piazza Fountain will produce the following effects. Base effects will always be produced. Bonus effects are determined by how many other unique Piazza Set buildings it is connected to.