A frozen water hose is dangerous and should not be used. If you are using a hose that has a metal or plastic tube, the hose will not freeze solid, but if it is a garden hose with a plastic or rubber hose, it can take several hours. The problem with freezing is that it's still liquid and will continue to expand as it freezes.This means that it can push on the walls of your pipe and cause leaks. If you do this in a small diameter pipe, then you can probably expect to have a leak somewhere along the line.