Combine 1 cup flour, baking powder, salt and sugar. In another bowl, combine egg, water and 1/3 cup lemon juice; stir into dry ingredients until smooth. , Place remaining 1/3 cup lemon juice and remaining 1/2 cup flour in separate shallow bowls. Dip fillets in lemon juice, then flour, then coat with egg mixture., In a large skillet, heat 1 in. oil over medium-high heat. Fry fillets until golden brown and fish flakes easily with a fork, 2-3 minutes on each side. Drain on paper towels. If desired, serve with lemon wedges.