For sauce, in a medium saucepan combine ketchup, water, onion, vinegar, molasses, Worcestershire sauce, chili powder, and garlic. Bring to boiling; reduce heat. Simmer, uncovered, for 10 to 15 minutes or until desired consistency, stirring often.
Trim fat from ribs. For a charcoal grill, arrange medium-hot coals around a drip pan. Test for medium heat above pan. Place ribs, bone-side down, on grill rack over pan. (Or, place ribs in a rib rack; place on grill rack.) Cover and grill for 1-1/2 to 2 hours or until tender, brushing occasionally with sauce during the last 10 minutes of grilling. (For a gas grill, preheat grill. Reduce heat to medium. Adjust for indirect cooking. Place ribs in a roasting pan, place on grill rack, and grill as above.) Pass remaining sauce with ribs. Makes 4 servings.