Combine sugar and water in a small saucepan and bring to a gentle simmer over medium heat, stirring until the sugar dissolves (about 2–3 minutes). Remove from heat.

Add the packed peppermint leaves to the hot syrup, pressing them gently with a spoon so they are submerged. Let steep for 20 minutes off the heat so the syrup extracts bright mint oils.

Stir in 1 tablespoon fresh lemon juice to brighten the flavor. Strain the syrup through a fine mesh sieve, pressing on the leaves to extract as much liquid as possible. Discard the solids.

Cool the syrup to room temperature, then chill in the refrigerator for at least 30 minutes before using. Refrigerated mint syrup will keep up to 2 weeks in a sealed container.

Assembly

Mix the beverage

In a pitcher, combine the chilled sparkling water, fresh lime juice and 1/4 cup of the prepared mint syrup. Stir gently to combine. Taste and adjust: add up to another 1–2 tablespoons mint syrup if you prefer sweeter/more minty, or more lime juice for brightness.

If preparing individual servings, place about 3/4 cup crushed ice into each of 4 tall glasses. Pour the mint-sparkling mixture over the ice evenly (about 1 cup per glass).

For a boozy version, add 1 1/2 tablespoons (about 22 ml) white rum to each glass before pouring the mixture and stir gently to integrate.

Garnish each glass with a fresh mint sprig and a lime wheel or wedge. For added aroma, clap the mint sprig between your palms before garnishing to release oils.

Serve immediately while fizzy and cold.