RecipesFastFood.COM – Watermelon margaritas are perfect for summer get-togethers, bachelorette parties or anytime you need a sweet way to relax after a hectic day. If you prefer not to use fresh watermelon, replace it with 2 oz. of watermelon syrup and add a splash of watermelon-flavored vodka. The Ingredients How to Make a Watermelon Margarita