Preheat oven to 375°F (190°C).
Peel, core, and slice the apples into about 1/4-inch thick slices.
In a large bowl, combine the apples, lemon juice, granulated sugar, cinnamon, nutmeg, and water. Toss to coat.
In a separate bowl, combine the flour, rolled oats, brown sugar, and salt.
Cut in the cold, cubed butter using a pastry blender or your fingers until the mixture resembles coarse crumbs.
Pour the apple mixture into a 9-inch square or round baking dish.
Sprinkle the topping evenly over the apples.
Bake for 45 minutes, or until the topping is golden brown and the apples are tender. If the topping starts to brown too quickly, tent the crisp with foil during the last 10-15 minutes of baking.
Let cool for at least 15-20 minutes before serving. Serve warm with vanilla ice cream, if desired.
