In a large heavy saucepan, bring the water, 2 tablespoons of the olive oil, and salt to a boil. Add the onions, gold potatoes, leeks, carrots, parsnips, turnips or rutabaga, celery root, fennel, and garlic. Simmer, half-covered, until the vegetables are very tender, about 30 to 35 minutes. Pepper liberally
Ladle into bowls and drizzle about 1/2 teaspoon of the remaining olive oil over each serving. The soup will keep for up to 4 days, covered, in the refrigerator.