"My friend is wanting water."
Translation:Tha mo charaid ag iarraidh uisge.
I'd say friend is quite intimately connected to a possessor: you're always someone's friend, after all, just like a hand is pretty much always someone's hand. You can apparently also use an caraid agam, but that'd imply a more distant relation than mo charaid. (In my mind's eye I actually see a child talking about their action figure called the "Caraid", but that's probably just me...) I don't think mo/do/etc. is becoming more common though, rather the opposite.