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.
If you own a building that uses groundwater you most likely have hard water which causes scale to form in your appliances. If that appliance is something you use to heat water for hydronic heating, the hard water may reduce their thermal efficiency and cost you more to operate in the long run. Many building owners will elect to install an ion exchange water softener to turn the hard water into soft water, and put a particle filter in front of the water softener to remove any suspended solids (like sand or silt).
If you're concerned about the quality of water going into the building for drinking purposes, then a membrane filtration system such as reverse osmosis would likely be installed. However, in places like China or India it's typically up to the individual tenant to install these systems and not to the building owner.