We've had some really dry and cold weather here in the last few weeks. The humidity in the house was down to about 35%, even with the humidifier going. With everyone bringing in Christmas trees right now you might notice that your cats are more than interested in the water for the tree. That's because they need to be 'watered' when the humidity is low too.
Rocky has been fine, but only because we feed him wet cat food with some water mixed in to dissolve one of this pills. Even so, I plan to keep an eye on his water dish and make sure it's full with fresh water at all times.