In a large saucepan, cook onion, carrot, and ginger in hot oil over medium heat about 8 minutes or until vegetables are golden, stirring occasionally.
Stir in water, chicken broth, pumpkin, salt, pepper, and the 1/8 teaspoon nutmeg. Bring to boiling; reduce heat. Simmer, uncovered, for 5 minutes, stirring occasionally. Cool mixture slightly.
Place half of the pumpkin mixture in a blender or food processor. Cover and blend or process until smooth. Repeat with remaining pumpkin mixture. Return all of the mixture to the saucepan. Heat soup over medium heat, stirring occasionally until hot.
To serve, ladle soup into bowls and top with a spoonful of sour cream; sprinkle with additional ground nutmeg. If desired, garnish top of soup with sweet potato chips.