Place the sliced apples in a 9x13 inch pan. Mix the white sugar, 1 tablespoon flour and ground cinnamon together, and sprinkle over apples. Pour water evenly over all.
Combine the oats, 1 cup flour, brown sugar, baking powder, baking soda, walnuts and melted butter together. Crumble evenly over the apple mixture.
Bake at 350 degrees F (175 degrees C) for about 45 minutes.
