In Mary Poppins (1964) Jane and Michael stipulate that their new nanny must:

Love us as a son and daughter, and never smell of barley water.

I've always wondered why they include this. If they mean actual barley water, which apparently is popular in various parts of the world (but not America), then it isn't really clear why the children hate it so much. It's not just that they don't want to drink it; they don't want to even smell it.

Part of me thinks they didn't mean literal barley water at all. They could also be referring (in a tongue-in-cheek way) to:

• Beer/ale. Usually made with barley, unpleasant to smell on someone, and of course means the person is drunk.

• Scotch. Made with barley (otherwise it's a different type of whiskey), not an unpleasant smell but also means the person is drunk.

Adults in the room would also recognize that, if the children specifically request that their nanny not show up stinking drunk, it would mean that it's happened before (further showcasing their parents' ineptitude at nanny-picking).

Is the "barley water" reference ever explained?