OK, I'll assume the US since my touring experience is limited to there...

I don't think I have ever been turned down when asking to fill up bottles with water AND ice from the soda fountain. I also have never been denied the use of the bathroom sinks with the exception of a very few places that said they did not have a public bathroom. I never ask without buying something first though.

I have had folks offer their own supply of bottled water in a few places that were either without running water or without palatable running water.

I have bought bottled water but only where the local water tasted really bad.

In the Sierras I carried a filter since it was often a long ways between tap water sources, but ice cold mountain streams were frequent.

I have not yet needed to knock on a door to get water from someones house, but have asked a couple times if they were already in the yard and they were always hospitable.

I love to use remaining snow on mountain passes to fill bottles and have cold water as a result.

A couple times I have had folks pull off on 100+ F days to offer an ice cold bottle.