Thanks! I was being facetious because I actually looked what they were after a few captchas. Indeed, there are many of those in my country but they don't look at all like that, typically being attached to the walls of the buildings, or covered underground.

To be pedantic, and risking your country being different to what I've personally seen around the world, what you see attached to the wall of a building isn't a fire hydrant.

These are standpipes [0] which can be used to move water to parts of the the building from that external fitting. They may contain some static water or be completely dry (like a dry riser [1]) but they are not a source of water like a hydrant is.

[0] https://en.wikipedia.org/wiki/Standpipe_(firefighting)

[1] https://en.wikipedia.org/wiki/Dry_riser

It was an interesting question for me as well, because I never stopped to think of why I didn't see these in certain cities abroad and how they fight fires in those cities.