I can't say it any more clearly and you are still cant follow along. It's not just the water source that comes into play when talking about water taste and people's tolerances.
Plumbing exists behind water fountains you say? Did you I thought they were fed by evaporators? Or maybe replicators from start trek?
I point you again to the toilet. Your toilet and refrigerator are also both fed from the same water supply... Just as the fountains, service stations, and toilets all are at Disney. But I don't think you'd argue Drinking from your toilet is the same as drinking from the water dispenser in your fridge.
If you can't grasp that - I'm done spelling it out at a 2nd grade level.
And public rest rooms are always on the municipal water... It's code. There aren't different supplies anywhere, grey water systems aren't anywhere in any of these types of facilities, and weee not talking locations on well water.
You are stating the obvious and missing the part of actual interest. It's not the source, but the handling, storage and dispensing differences you are closing your eyes to.