If making a sugar rim, pour sugar onto a small Plate. Rub rim of a Drinking Glass with lime wedge and press rim into sugar. Reserve lime wedge.

Fill a cocktail shaker about halfway with ice cubes. Add tequila, pomegranate juice, lime juice, and simple syrup (if using). Shake vigorously until outside of shaker is very cold, 15–20 seconds.

Fill glass with ice and strain margarita into glass. Top with sparkling water and garnish with reserved lime wedge.