(Brit here) I found that when I asked for a glass of water in a US restaurant that they didn't understand me. I had to use a 'D' sound instead of a 'T' and then things were fine. This is different again from the glottal stop version (wa'er) which would be universally understood (if not liked) in the UK.

On that note, I'm reminded of the George Bernard Shaw quote " it is impossible for an Englishman to open his mouth without making some other Englishman despise him."