We took a road trip through Mississippi. The drinking water EVERYWHERE tasted like swamp. Restaurants, homes, etc. Everyone was serving it, and everyone was drinking it. Even the soda fountain was tainted. Everyone looked like us as if we were crazy. You could smell your glass before you got it to your mouth. This wasn't an isolated area.
Point being, some people have different tastes, and the 20M people you speak of might find PNW water gross... I'm not sure. But I am convinced some people don't notice the same tastes that others do, based on what they were raised with.
I also generally cannot stand lake fish, but I keep trying them!