Optional: For a fun twist, run a lime wedge around the rim of your glass and dip it in salt or sugar.
Add the lime juice, grapefruit juice, simple syrup, and a pinch of salt to a glass. Stir to combine. Add ice and top with sparkling water.
Alternatively, if you have a cocktail shaker, combine the lime juice, grapefruit juice, simple syrup, and a few ice cubes. Shake well for 10–15 seconds, then strain into a glass filled with fresh ice. Top with sparkling water and give it a gentle stir.
Garnish with a lime wheel or grapefruit wedge, if desired.
