In a small saucepan, bring the water to a boil over moderate heat. Add the sugar and vanilla and simmer until a light syrup forms, about 15 minutes. Let cool for 10 minutes.
Pour the warm syrup into a large bowl. Gently stir in the fruit and let macerate at room temperature for several hours, stirring occasionally. Refrigerate the fruit salad until chilled. Garnish with purple basil leaves just before serving.