In a medium saucepan, heat water with sugar over medium-high heat, stirring occasionally until sugar is dissolved. Simmer, uncovered, for five minutes. Remove from heat and stir in mint leaves. Let stand 20 minutes

Meanwhile, peel kiwifruit and cut into chunks. Puree in a food processor. Place puree in a pitcher. Strain cooled syrup into pitcher, pressing on mint, then discard leaves. Refrigerate until cold. Squeeze juice from 2 lemons. Stir into kiwifruit mixture. Taste, squeeze in juice from remaining lemon for a more tart lemonade.

Pour into glasses. Top with sparkling water. Serve garnished with a slice of kiwifruit.