Because it is difficult to dissolve sugar in cold liquid, bartenders use a sugar solution called simple syrup. It is easy to prepare and keeps 2 months or longer in the refrigerator.
In a small saucepan over medium-high heat, bring the water to a simmer. Add the sugar and stir until it completely dissolves. Remove the pan from the heat and set aside to cool to room temperature. Pour the syrup into a clean 1-pint bottle, cap it and refrigerate until ready to use.
Makes 1 1⁄2 cups.