In a medium saucepan combine water and sugar; bring to boiling,stirring frequently. Boil gently, uncovered, for 2 minutes. Remove from heat and cool slightly.

Place the watermelon and berries in a blender or large food processor; cover and blend or process for 30 seconds. Add the warm syrup and blend until almost smooth. Transfer the mixture to a 3-quart rectangular baking dish or a 13x9x2-inch baking pan. Place in the freezer, uncovered, for 1-1/2 hours or until almost solid.

Remove sorbet from freezer. Using a fork, break up the frozen fruit into a somewhat smooth mixture. Stir in snipped lemon balm. Freeze 1 hour more*. Break up the ice with a fork and serve in shallow bowls.Top with lemon balm sprigs and a few blueberries and/or raspberries. Note: If mixture is frozen longer than the final hour, let it stand at room temperature about 20 minutes before breaking up mixture with a fork and serving.