Peel and core apples. Cut into thin slices. Layer apple slices over base of a medium pie dish (6-cup capacity).
Using fingertips, rub butter, flour and sugar together in a large bowl until mixture resembles breadcrumbs. Add water and mix well (mixture will appear curdled at this stage). Spoon mixture over apples in pie dish.
Cook in a moderately hot oven (190C) for about 1 hour, or until top is golden brown and apples are tender.