Preheat oven to 350°. Coat a 9-inch square baking pan with cooking spray.
Cut croissants in half lengthwise. Spread about 1 tablespoon of preserves on each half. Replace tops, and cut croissants into small strips. Place strips in baking pan. Dab remaining preserves on top.
Whisk eggs, then whisk in milk, water, butter, vanilla, and cinnamon. Pour mixture over croissants. Press croissants into liquid if necessary. Let set for 5 minutes.
Bake until a knife or pick inserted in the center comes out clean (about 45 minutes). Allow to cool for 15 minutes. Sprinkle with confectioners sugar or whipped cream, if desired.