Anti-freeze or drain?

There should be coolant in every car regardless of your location. (except for may be a race car where you can't run antifreeze) Antifreeze combats freezing, helps with overheating, has lubrication for your water pump, and has chemicals to prevent corrosion. A 50/50 mix is recommended but if you just drain the radiator some water is left in the block so I would drain the radiator and add a gallon of pure anti freeze. Run the engine and test the antifreeze. I would make it safe to -30° by draining and adding as needed to get there.