Turn off the main water supply to the house. Also, close the supply valve to your water heater, just to isolate it.

Open an interior tap. Backfeed compressed air (about 20-40PSI) into the spigot. This will push the water down the supply piping.

When air starts spitting out of the interior tap, close the ball valve for the exterior line. Turn on the house supply, wait for the air to burp out, then shut off the interior tap and open the water heater.