In a small saucepan, combine the water, sugar, and rosemary leaves. Bring to a boil and stir to dissolve all the sugar. Bring to a simmer for a couple of minutes and remove from the heat and let steep for 30 minutes.
Using a strainer, pour syrup into a jar to remove the rosemary leaves. Smaller bits of rosemary are fine. Let cool and store in the refrigerator for up to two weeks.