If you enjoy a salted glass, prep the rim of your lowball glass by rubbing a lime wedge along the rim. Dip in tequila salt, and set aside.
Shake:
Add the tequila, triple sec or Cointreau, blood orange juice, lime juice, and a handful of ice inside of a shaker. Shake vigorously until the sides are fully frosted.
Serve:
Pour the cocktail it into the prepared glass. Top off with sparkling water to make it a taller cocktail. Garnish with a fresh blood orange slice.