To make simple syrup, combine sugar and water in a small saucepan. Stir over medium-heat until the sugar dissolves and the mixture boils, then lower heat to medium and simmer for 2-3 minutes. Remove pan from the heat and cool to room temperature. Pour syrup into a sealed glass container and store in the fridge until ready to use.
To make limeade, combine lime juice, sparkling water, and about ¾ cup simple syrup in a large pitcher. Stir to combine. Taste, and add more simple syrup if you desire a sweeter drink.
Add ice, lime slices or wedges, and mint leaves for garnish, as desired. Serve cold!
Simple syrup will keep for a month in the fridge, and is very useful for sweetening other beverages as desired, to include cocktails!