Slice 1-2 jalapenos (depending on your spice preference) and place them in a small pot with 1.25 cups of water. Bring to a boil, then lower the heat and allow it to simmer 5 minutes.
Strain the water into a jar and add 1 tablespoon of liquid monk fruit sweetener. This can be stored in the fridge for several weeks.
To make the margarita
In a blender, combine the tequila, lime juice, simple syrup, and watermelon. If you want a frozen margarita, add a glass full of ice as well.
Blend until the watermelon is blended and well incorporated with the liquid (or if using ice, until you reach your preferred slushie consistency).
Salt the rim of a glass and fill it with ice if you're serving your margarita on the rocks. Pour the margarita, top with sparkling water, and serve immediately.
Notes
*Optional orange sparkling water: This adds a hint of orange to replace the missing Triple Sec that most margaritas might have. It adds some bubbly and makes it more of a sparkling margarita. You can leave this out if you prefer!This recipe makes one margarita with 3.4 net carbs.