RIM GLASSES. Wet glass rims and dip in granulated sugar. I typically just wet glasses with water, but depending on the type you're using a simple syrup or agave sweetener could also work as a sticky rim adhesive.
MAKE LEMON-INFUSED SPARKLING WATER. Fill SodaStream bottle with water & add 1/2 tsp SodaStream Lemon Fruit Drops. Insert bottle into Sodastream Fizzi Sparkling Water Maker & press down for 2 seconds. Repeat 3x to add carbonation to water.
MAKE COCKTAIL. Fill rimmed glasses with ice (I suggest 3-4 small cubes). Add gin, lime juice, red grapefruit juice, agave sweetener & more ice to shaker. Shake vigorously to mix and strain into rimmed glasses. Top glass with SodaStream lemon-infused sparkling water.
GARNISH. Feel free to garnish glasses with a red grapefruit wedge and a sprig of rosemary.