Preheat oven to 350. Place the sliced apples in a 9 x 13" pan. Mix the white sugar, 1 tbsp. flour and cinnamon together and sprinkle over apples. Pour water evenly over all.
Combine oats, 1 cup flour, brown sugar, baking powder, baking soda and melted butter together. Crumble evenly over the apple mixture. Bake at 350 degrees for about 45 minutes.