Combine cake mix and oats in a large bowl; stir in the melted butter until the mixture is crumbly. Measure half of this mixture (about 3 cups) into a greased 13x9x2-inch pan. Press firmly into pan to cover the bottom.
Combine preserves and water; spoon over crumb mixture in pan, and spread evenly. Cover with remaining crumb mixture. Pat firmly to make top even.
Bake for 20 minutes; top should be very light brown. Cool completely before cutting into bars.