If the dog is not severely dehydrated, you can use a syringe to draw water or sugar water, and then inject it into the dog's back molars. This will allow the dog to drink the water. When injecting, be careful not to push it too fast, and not once. Push too much or your dog will choke easily. If the dog is severely dehydrated and has gone into shock, it is best to take the dog to a pet hospital for treatment immediately to avoid life-threatening injuries.