Heat oil in a large Dutch oven over medium heat. Add onion, and sauté 3 minutes. Add garlic, and sauté 1 minute. Stir in 1/4 teaspoon salt.
Add water and potato; bring to a boil. Reduce heat, and simmer, uncovered, 8 to 10 minutes or until potato is tender. Add broth, crushed red pepper, and sausage; bring to a boil. Reduce heat, and simmer, uncovered, 10 minutes. Stir in remaining 1/4 teaspoon salt and kale, and simmer 8 to 10 minutes or until kale is tender.