In a nutshell: "Janitor".

Ooo this is a hard question because there isn't really like a sole occupation for this. I think in an office setting it would be a receptionist who helps maintain the cleanliness of the lobby. They may offer you water as you wait to meet whoever you came to meet. If there is a big spill or a pipe suddenly bursts then they'd call facility services to clean up the mess. In a school setting, big spills, messes/graffiti would be again facility services aka custodians. In fancy school places like boarding school there are ground keepers who keep you know the grass trimmed and proper and things working amongst other things. Hope this answers your question!

The person who looks after the grounds is a caretaker. The person who cleans is a cleaner. These days, there isn't a person to make tea. Nobody really serves the employees. There isn't a collective term for these people that I can think of.

You could just say assistant.

The exact term for a person who works at a school (to clean the premises including bathrooms) is custodian.