It really depends on the status of the systems on board. There are air-conditioning/humidifying packs onboard and you could have a situation where one or more can be unserviceable. Back in the early days of the 787 operations, for a brief moment there was a situation when - in certain conditions - the whole thing would go mental and start dripping water on customers. I remember it being quite a problem on JAL, who was an early adopter. Boeing introduced some fixes and, for whatever reason, on one 787 they didn't work. We ended up with an extremely dry cabin on that flight, and it was rough!