Melt the butter in a Dutch oven over medium-high heat. Add onion, celery, and parsnip; sauté 10 minutes. Stir in the wine, scraping pan to loosen browned bits. Add water, salt, pepper, broth, potato, and bay leaf. Bring to a boil; reduce heat to medium. Cook 20 minutes or until the vegetables are tender. Discard bay leaf.
Place one-third of vegetable mixture in a blender, and process until smooth. Pour puréed vegetable mixture into a large bowl. Repeat procedure with remaining vegetable mixture. Stir in the lemon juice. Spoon 1 cup soup into each of 6 bowls; top each serving with 1 tablespoon sour cream and 1/2 teaspoon parsley.