Separate and peel garlic cloves. In large saucepan, heat oil over medium heat; fry garlic, onion, salt and pepper, stirring, until onion is softened, about 5 minutes.
Add stock, carrots, potato and water; bring to boil. Cover, reduce heat and simmer until vegetables are tender, about 20 minutes.
Using immersion blender or in batches in blender, purée soup until smooth. Add water to thin, if desired.