Open can of lychees and drain, reserving syrup. Set fruit aside to use as garnish. Fill cocktail shaker with ice, then add 1 cup lychee syrup along with lemon juice and rosewater. Shake for 15-20 seconds. Pour into 3 cocktail glasses and top with sparkling water. Add a lychee to the bottom of each glass and garnish with a rose petal. Drink up!