On a recent business trip to Las Vegas, I was acutely aware of how dry the air was. I wanted to make sure I was hydrated but I forgot to pick up some saline solution and there was none for sale at the hotel.
As I was chatting with a colleague about the air, he agreed, and clued me in to a little known Las Vegas hotel secret. He told me that most hotels actually have humidifiers (knowing how dry the air is) and will send one to your room if you ask. I went to the concierge desk at the Paris where I was staying and he directed me to call housekeeping, and sure enough they sent one up.
Keep in mind that not every hotel will have humidifiers available, so when booking your hotel you might want to ask in advance if this is a concern for you.
Also, there are travel humidifiers that you can purchase if you want your own, and of course saline solution is a great thing to keep on hand. If your hotel does sell it, I am sure it will be pricey (like my $4 bottle of water at the gift shop.)