Like I said, in extremis. The same way you might ask to use a bathroom at a business you were not a customer at, or to borrow something from a stranger to solve a clear temporary need.

The sort of request that is granted with a smile if asked politely, and denied if asked rudely, basically. Part of the general fabric of society.

You would only ask if you'd been out a while on a hot day and were parched, or something similar. There's surely some social analogue not involving water where you live?