Nothing beats cooling off like a refreshing Watermelon Key Lime Slushie. With only 4 ingredients this is one simple recipe to make. Be sure to try my Raspberry Lemonade Slushie that is just as refreshing. Watermelon Key Lime Slushie Watermelon Key Lime Slushie Recipe Type: Beverage Author: Shortcut Saver Serves: 3 1/2 cups Ingredients 3