Sort and wash beans; place beans in a large pot add enough water to cover the beans by more then three inches, one teaspoons salt (salt added during soaking tenderizes the bean skins), cover and soak over night.
Drain beans, and return to pan. Add the 5 cups water, onion, and garlic; bring to a boil.
Cover, reduce heat, and simmer until tender.
Drain beans in a colander over a bowl, reserving cooking liquid.
Combine 1-1/2 cups cooking liquid, chili powder, cumin, pepper, and salt in the pan. Add half of the beans, and mash.
Stir in remaining beans; cook over medium-low heat 5 minutes or until thickened, stirring occasionally. If beans become to thick, add additional cooking liquid a little at a time until desired consistency is reached.