Combine 1/2 cup granulated sugar and 1/4 cup water in a small saucepan over medium heat. Stir frequently until the sugar fully dissolves and the liquid just reaches a gentle simmer (about 3–4 minutes). Do not boil vigorously.

Remove the saucepan from the heat. Stir in 2 tablespoons fresh lemon juice, 2 tablespoons fresh lime juice, 1 teaspoon lemon zest and 1 teaspoon lime zest. Let the mixture steep for 10 minutes at room temperature to extract bright citrus oils.

Strain the syrup through a fine-mesh sieve into a small bowl or jar to remove zest and any solids. Allow to cool to room temperature. The syrup can be refrigerated in a sealed container for up to 1 week.

Soda Base

Assemble the drink

Fill a tall glass with about 1 cup of ice cubes. Pour in 2 tablespoons of the prepared citrus syrup (adjust 1–3 tbs to taste).

Add 2 cups of chilled club soda or sparkling water. For a sweeter, more soda-like final drink, add 1/2 cup chilled lemon-lime soda (like Sprite or 7-Up) instead of part of the club soda — stir gently to combine without flattening the carbonation.

Taste and adjust: if you prefer sweeter, add up to 1 more tablespoon citrus syrup; if you prefer tarter, add a splash (1/2 tsp) more fresh lemon or lime juice.

Finishing & Garnish

Garnish with 1 lemon slice and 1 lime slice on the rim or floated in the glass. Add 1–2 sprigs of mint if desired and give a gentle clap between your palms before adding to release the aroma.

Serve immediately with a straw. Stir lightly before drinking to lift any settled syrup.