It depends on how long it will be that cold. Is it too early to look at the hourly forecast? If it just dips down for an hour or two, I wouldn't worry. We've left ours hooked up and had no freezing inside. The only problem we had was that the water didn't want to flow first thing in the morning because there was some slush in the hose. The first bad thing to happen would be the hose freezing and bursting. That would happen before any damage to your internal plumbing as I assume you will have some heat going. If you want to be very careful, you could take the pressure off your hose or disconnect, but no need to go further than that. My opinion.