Preheat your oven to 180°C (350°F).
In a large mixing bowl, combine the sliced apples, granulated sugar, ground cinnamon, lemon juice, and water. Toss the mixture until the apples are evenly coated.
Transfer the apple mixture into a baking dish or pie dish (approximately 20cm x 20cm or equivalent), spreading it out evenly.
In another mixing bowl, prepare the crumble topping. Combine the all-purpose flour, rolled oats, cold cubed butter, brown sugar, and a pinch of salt. Use your fingers or a pastry cutter to rub the butter into the dry ingredients until it resembles coarse breadcrumbs.
Sprinkle the crumble mixture evenly over the apple filling in the baking dish.
Place the baking dish in the preheated oven and bake for about 35 minutes or until the crumble topping is golden brown, and the apple filling is bubbling around the edges.
Remove the apple crumble from the oven and allow it to cool slightly before serving. It's delicious on its own, but you can also serve it with a scoop of vanilla ice cream or a dollop of whipped cream for an extra treat.Enjoy your homemade apple crumble!