In a medium saucepan melt butter. Add onion, saute until tender about 5 minutes. Pour in water and bring to boil. Add carrots and potatoes. Return to boil. Reduce heat, cover and simmer 20 minutes or until vegetables are tender. Remove from heat and let cool slightly. Place mixture in blender container and blend until smooth. Return to pan; stir in milk and seasoning. Heat but do not boil. Serve hot. Makes 4 servings.