In a small bowl, sprinkle the gelatin over the water and let stand until softened, about 5 minutes. Scrape the gelatin into a small saucepan. Add the granulated sugar and the remaining 1 cup of cream and cook over very low heat just until the sugar is dissolved, about 2 minutes. Let cool completely, then whisk in the lychee puree. Pour the panna cotta into 8 Champagne flutes and refrigerate them until they are set, about 4 hours.