Add all ingredients to a blender or food processor and blend until smooth. Make sure there are no chunks of watermelon remaining.
Pour the mixture into a freezer safe pan (glass or metal work well). Then, place it in the freezer for one hour.
Remove the pan from the freezer. Using a spoon or a fork, gently stir the ice crystals that have formed, dislodging them from the edges and breaking up any large chunks. Return the pan to the freezer for another hour.
Remove the pan, and scrape down the ice. This ice will start to become thicker and chunkier, so be sure to break down all of the chunks. Return the pan to the freezer for one more hour.
Remove the pan and scrape the ice again. This time, use a fork to scrape the ice into small pieces, almost like you’re “shredding” the ice. The ice should be fluffy, with a snow cone like consistency.