Add fresh lemon zest, fresh orange zest and dried edible rose petals to the simmering syrup. Reduce heat to low and let the mixture steep gently for 5 minutes, stirring occasionally to release citrus oils and floral notes.

Turn off heat and stir in fresh lemon juice and rose water. Allow syrup to cool in the pan for 10 minutes to continue infusing, then strain through a fine mesh sieve into a heatproof container to remove zest and petals. Chill syrup in the refrigerator until cold (about 30 minutes) or use at room temperature if short on time.

Cooler Assembly

Prepare glassware: fill a large pitcher or 4 individual glasses with the ice cubes (2 cups total will fill a pitcher; adjust for individual servings).

Muddle mint: place half the mint leaves in the bottom of the pitcher or each glass and gently bruise with a muddler or the back of a spoon to release aroma. Do not over-muddle — just press once or twice.

Add juices and syrup: pour the chilled fresh grapefruit juice (1 cup) and fresh lemon juice (2 tbs) into the pitcher or glasses. Add 4 to 6 tablespoons of the chilled citrus rose syrup to the pitcher (about 1/4 to 1/3 cup) depending on desired sweetness and floral intensity. If using individual glasses, add about 1 to 1 1/2 tablespoons syrup per glass.

Top with sparkling water: slowly pour the chilled sparkling water (3 cups) into the pitcher to preserve effervescence. Stir gently once to combine; avoid vigorous stirring which will flatten bubbles.

Taste and adjust: sample the cooler and add more citrus rose syrup if you prefer sweeter or more floral notes, or a squeeze of lemon for brighter acidity.

Serve: pour into glasses if mixed in a pitcher. Garnish each glass with a thin grapefruit or lemon slice, a few mint leaves, and a fresh rose petal if using. Serve immediately while sparkling and cold.