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

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) https://en.wikipedia.org/wiki/Standpipe_(firefighting) [1] https://en.wikipedia.org/wiki/Dry_riser https://en.wikipedia.org/wiki/Dry_riser