Cast iron tea kettle? Apparently.

So they have cast iron tea kettles, apparently. They are said to keep your coffee or tea hot. They're common in Japan.

They're also used on top of a wood stove, to humidify the air in the winter. In South Louisiana, there's definitely no need for a humidifier.

I would be concerned about leaving liquid in cast iron for long periods of time, due to rust.

The model pictured above, has an enameled interior to prevent rust. Not all of them do. If you intend to drink out of it, I'd recommend the enameled interior.

If it's just to humidify the air, then you might not need enameled, but I would still dry it regularly.