Heat an extra-large soup kettle over medium-high heat. Add the sausage and brown, breaking it up with a spoon. Add the onion and garlic, and saute 3 minutes. Stir in the tomatoes, breaking them up with the spoon. Stir in the stock and 1 quart of the water, and raise the heat to high. Bring to a boil, add the pasta, and cook, stirring, for 5 minutes. Then add spinach, beans, and remaining quart of water. Cover and simmer for a few minutes longer, stirring occasionally, until spinach is tender. Add salt to taste.