Rinse dry beans. In a Dutch oven combine rinsed beans and the 5 cups cold water. Bring to boiling; reduce heat.

Simmer, uncovered, for 10 minutes. Remove from heat.

Cover and let stand for 1 hour. Drain and rinse beans.

In a 3-1/2- or 4-quart slow cooker combine beans, broth, the 1/2 cup water, the onion, garlic, cumin, and cayenne pepper.

Cover and cook on low-heat setting for 8 to 10 hours or on high-heat setting for 4 to 5 hours

Stir in undrained tomatoes; cover and cook for 30 minutes more. If desired, partially mash mixture with a potato masher, leaving soup chunky. If desired, top individual servings with cilantro.