In the UK (and I dare say much of Europe) its not at all uncommon to ask for a tap water at a restaurant. I drink around 2 litres of tap water a day, have done all my life.
Having been to a fair few places in the US I can see why people dont want to drink it, it stinks and tastes pretty awful. How you manage to take pure natural water and make it taste like feet is beyond me.
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.
Hoestly, the savings for the economy in terms of wasted electricity from scaled up kettles and the reduction in chemicals needed to remove the near instant buildup of limescale would be worth it 10 times over.
It was very noticeable when I passed through Dubai airport and tried to fill up a water bottle. I tried several cafes and all told me they don't do that, I'd have to buy bottled water. I've never been refused that in the UK when asking politely. Ended up finding the water fountains, but I think there was only 1 fountain per terminal, and 2/3 weren't working when I visited.
But of course, it’s a convenient excuse to sell bottled water. Not impossible to have water delivered for a drinking fountain.
And the water tastes salty.