I legitimately do not understand why so many people refuse to drink tap water. I get that an occasional bottle of water is convenient when traveling or something, but some of my neighbors seem to only drink bottled water even at home. The city will literally test your water for free if you don't trust it for some reason.
You should go on street view and check out Asia, whenever I visited Thailand and see a backroad, there is a huge number of used plastic bottles lying next to the road.
They still get drinking water from bottles.
Weather that is the case in large cities like Bangkok I don't know as I haven been there enough to learn.