The technology most commonly used for a local drinking water treatment plant in a building (such as an apartment, hotel, office tower, etc.) is going to be a particle filter paired with an ion exchange water softener. But it is also going to depend on just how bad the incoming water quality is.
In a lot of places, the incoming water quality isn't bad at which point the building owner won't choose any treatment. These places probably get their water from surface sources such as lakes.