Place the sliced apples in a 9x13 inch pan. Mix 1/2 cup granulated sugar, 1 tablespoon of flour and 1/2 teaspoon ground cinnamon together, and sprinkle over apples.
Pour water evenly over all.
Combine the oats, 1 cup flour, brown sugar, 1/4 teaspoon baking powder, 1/4 teaspoon baking soda, and 1/2 teaspoon ground cinnamon. Stir to blend. Mix in melted butter until the mixture is crumbly. Sprinkle evenly over the apple mixture.
Bake in preheated oven for about 45 minutes, or until the top is golden brown.