The water in some parts of the US has natural chemistry that makes it unpleasant to drink even though it is safe. California urban areas are notorious for this, as an example. In principle you could remediate the water to make it taste good and remove any discoloration (also a thing in a few regions) with enough industrial processing but that would greatly increase the cost of already expensive tap water.
People who grew up in one of these areas are habituated into never drinking the tap water even if they move to a city with excellent tasting and very high quality tap water. I’ve lived in extreme examples of both.
You also see the opposite case, where someone who grew up with amazing tap water naively grabs a glass from the tap in north San Diego and has a “wtf is this” moment.
San Diego's tap water tastes truly awful. The first time I ever traveled to another city (Denver), I was forced to drink the tap water and could not believe how good it tasted.
San Diego has the worst tap water for drinking I have ever experienced in the US. When I lived there, pretty much everyone had a reverse osmosis system installed to make it drinkable.
Fortunately, I live in the Pacific Northwest currently, which generally has some of the best tasting water you’ll find anywhere. No one would dream of not drinking the tap water.
People who grew up in one of these areas are habituated into never drinking the tap water even if they move to a city with excellent tasting and very high quality tap water. I’ve lived in extreme examples of both.
You also see the opposite case, where someone who grew up with amazing tap water naively grabs a glass from the tap in north San Diego and has a “wtf is this” moment.