"But Tank, it's December! The water would freeze!"
This is an unreasonable action for carolers and is considered de rigeur.
Emily Post's viewpoint says that traditionally, carolers need to have boiling oil poured on them as per the castles in Europe where the trend originated.
In modern times, if you can't procure boiling oil, a well-made wax melter can give a nice, large deluge of molten wax onto the carolers to honor this time-honored tradition. Try adding a more wintry, holiday scent and your carolers will appreciate the thought all holiday season.