Sparkling Limeade (L?monada)

1/2 cup granulated sugar or more, to taste
1 1/2 cups freshly-squeezed lime juice
1 quart sparkling water

Beginning with the 1/2 cup sugar, add to the lime juice and stir until the sugar is dissolved. Add the sparkling water, stir and taste for sweetness; add more sugar if needed. Pour over ice to serve.