Combine the carrots, broth, water, onion, ginger and salt in a small pot.
Bring mixture to a boil.
Reduce heat to a low boil and cook for 20-25 minutes until carrots are easy to smash when pressed against the side of the pot with the back of a spoon.
Transfer soup to a food processor or blender or use immersion blender and process until smooth.
Top with green onion, if desired.