Preheat the oven to 350 degrees F (175 degrees C). Grease four 12-cup mini-muffin tins.

Mix apples, water, white sugar, and 1/2 teaspoon cinnamon together in a medium saucepan; bring to a simmer over medium-low heat, stirring occasionally. Simmer until apples are partially cooked, about 5 minutes; remove from heat.

Combine flour, oats, brown sugar, remaining 1 teaspoon cinnamon, and nutmeg in a large bowl; cut butter into flour mixture with a pastry cutter until mixture resembles coarse crumbs.

Press a heaping tablespoon of crust mixture into each muffin cup to cover bottom and sides of cup; patch holes with crust mixture.

Place about 2 teaspoons filling in each cup. Crumble about 1 teaspoon of remaining crust mixture on top.

Bake in the preheated oven until golden brown, 15 to 20 minutes.