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