. Almost every hotel room has one and it can tell you a lot about how detail-oriented the housekeeping is.
Because coffeemakers and electric kettles constantly have water or moisture in them, they can be a haven for bacteria, rust, and mold. If they aren't cleaned regularly — and I mean with vinegar, not rinsed with hot water — they quickly become gross. As such a small item and a tedious one to clean, I've found that coffeemakers and electric kettles are frequently overlooked by less diligent hotels.
Even if the kettle is cleaned regularly, with frequent use, some amount of rust is unavoidable. But that's frequently a signal that a room or rental needs some sprucing up. When I get to a new hotel room, I pop open the top to the appliance. If I see mold or rust, which happens often, I ask for a new room or shorten my stay to one night and move on to a different place.
If they're leaving a rusted kettle in the room, it's a signal to me that no one is keeping a close eye on the room's long-term upkeep. If there's mold in the coffeemaker or kettle, what else hasn't gotten a thorough cleaning?
People clean their nylons in them.