Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 2 quart casserole dish.
In the casserole dish, alternately layer the sweet potatoes and apples.
In a medium saucepan over medium heat, mix together brown sugar, 1/3 cup water, cinnamon, raisins, butter and salt. Cook 5 minutes.
In a small bowl, stir together remaining water and flour. Combine with the brown sugar mixture. Pour over the sweet potatoes and apples. Place the lemon slices on top.
Bake covered in the preheated oven 20 minutes. Uncover and continue baking 20 minutes, or until the sweet potatoes and apples are tender.