Cool down from the summer heat with this ultra refreshing Watermelon Key Lime Slushie recipe made from real fruit! Watermelon Key Lime Slushie (Yield about 3 1/2 cups) INGREDIENTS 3 cup Watermelon cut in cubes. 6-8 Key Limes 1/4 cup Sugar 2 cup Ice DIRECTIONS Place watermelon in freezer for 1 hour. Zest key limes