Cut onions into 1/4-in. slices; separate into rings. Place in a large bowl; cover with buttermilk and soak for 30 minutes, stirring twice. , In a shallow dish, beat eggs and water. In another shallow bowl, combine the flour, salt, chili powder, cayenne, sugar, garlic powder and cumin. Drain onion rings; dip in egg mixture, then roll in flour mixture., In an electric skillet or deep-fat fryer, heat 1 in. of oil to 375°. Fry onion rings, a few at a time, for 1 to 1-1/2 minutes on each side or until golden brown. Drain on paper towels.