Preheat oven to 375°F (190°C).
Place the sliced apples into a greased 8-inch square baking dish and pour water over them.
In a medium bowl, mix brown sugar, flour, oats, butter, cinnamon, nutmeg, and salt until crumbly.
Sprinkle the mixture evenly over the apples.
Bake uncovered for 40–45 minutes, or until the topping is golden and apples are tender.
Serve warm with vanilla ice cream or whipped cream if desired.