The US is a big place and water sources vary widely from place to place. Springs usually have the best tasting water but are relatively rare as municipal water sources. My hometown used a well as a water source and the town to our north used a river. Our water always had a bit of sulfur taste to it (as did my family's private well for agriculture) but the city next to us didn't have that taste. Our city was small and couldn't afford the infrastructure to get the sulfur content down and we didn't have river access.

The intended moral of the story is, while I am unfamiliar with the UK I suspect that water distribution is likely far more centralized there as the place is much smaller overall vs the US and more densely populated than most areas in the US. Higher population density means more money to build the facilities to have better tasting water. Plus a centralized administration would result in a more homogeneous quality across the region. Here in the US, each city typically runs its own water system with little to no state involvement other than periodic inspections for standards compliance.