How to Make It
For Simple Syrup: Combine the watermelon and sugar in a small saucepan over medium heat. Use a potato masher or another utensil to mash the watermelon and sugar together, pushing out the liquid and dissolving the sugar. Simmer for 5 minutes, stirring frequently. Pour the mixture through a fine mesh sieve set over a bowl or jar, pressing the watermelon to extract all the liquid. Set aside to cool completely. Makes just over 1 cup of simple syrup.
For Watermelon Juice: Combine the watermelon and water in a blender. Blend until smooth, pour through a fine mesh sieve set over a bowl or jar.
Combine the tequila, watermelon juice, lime juice, and simple syrup in a cocktail shaker with ice. Shake until thoroughly chilled, about 30 seconds, and pour into glasses rimmed with lime juice and coarse salt. Garnish with lime wedges and serve imediately.