Most times you should have freezing temps for just a short period of time and with the furnace set a 50 at night should have no problem. We keep the water heater on electric so there is always warm water in that. We don't shut it off and on as it would seem to us that letting the water get really cold uses as much energy to get it hot again as it does to let the tank periodically run to just keep the water hot. And that helps those lines stay warm. If really cold, we leave our cabinet doors open in areas with plumbing so the heat from inside can get to those areas easier.