In a bowl, combine 1 cup flour, baking powder, salt and sugar; set aside. Combine egg, water and 1/3 cup lemon juice; add to dry ingredients and mix until smooth. Dip fillets in remaining lemon juice, then remaining 1/2 cup flour; and finally coat with batter. Heat 1 inch of oil in a skillet. Fry fish, a few fillets at a time, over medium-high heat for 2-3 minutes on each side or until the fish flakes easily with a fork. Drain on paper towels. Garnish with lemon wedges, if desired.