Soak the beans in water overnight. Drain the water and replace with fresh water. Simmer, covered, for 1 - 1 1/2 hours. Drain and put beans in a baking dish. Add the onion, garlic, mustard, ketchup, and water. Mix and cover. Place in a preheated 300-degree oven. Bake for 3 - 4 hours, mixing occasionally.