Preheat the oven to 350 degrees F (175 degrees C). Combine 3 tablespoons sugar and cinnamon in a bowl.
Layer apples in an ungreased 9×13-inch baking pan, sprinkling each layer with cinnamon-sugar.
Combine flour, 1 cup sugar, egg, and baking powder with a fork. Sprinkle over apples. Lightly sprinkle water over top.
Bake in the preheated oven until topping is golden brown, about 30 minutes.