Cut a watermelon into chunks until you have approximately 4-5 cups. Add the watermelon to a blender and blend until smooth. Pour the purée through a mesh strainer into a measuring glass.

In a shallow bowl or on a plate, combine sea salt and chili powder. Take a lime wedge and run it along the rim of the glasses then coat the rims in the chili salt.

Add half of the watermelon juice, 1 1/2 tablespoons lime juice, 3 tablespoons tequila, 2-4 jalapeño slices and a handful of ice to a cocktail shaker. Shake until combined and cold. Add extra tequila, watermelon juice, or lime juice depending on your taste. Repeat this process for the second margarita.

Pour the margarita into the prepared glass with ice. Top off with sparkling water if desired and 2-3 jalapeño slices. Garnish with a lime and serve.