I grew up in NYC. Their municipal water was noted as one of the best in the world. The water was really very good up until the 90’s. Somehow the quality went downhill and I can’t explain it. The city gets its water from the Catskill reservoirs.
Mostly old sewage treatment plants dumping into those reservoirs and runoff. Ummmm...tasty!
The water starts out in the reservoir. Then it gets treated with chemicals before being run through a few hundred miles of pipe. Pipe that is decades old, rusty, leaky and maintained by the best union labor available.