Hook up a hose or fill fresh water tank in cold weather ?

We usually travel with a full or near full fresh tank, and even in good weather it's not unusual for us to skip hooking up the water hose for a one or two night stop over. And I have seen folks wake up with frozen water hoses, even when the park had a sign posted at check-in advising unhooking due to cold weather and a park employee had come around advising everyone they saw of it. One camper told me he didn't think it would freeze because the hose was connected to a freeze proof faucet! Amazing...