2tbspcitric acid (available at Amazon and elsewhere)
Instructions
Combine all the ingredients in a small pan. Bring to a simmer until the sugar has melted.
Pour into a blender and blend (remove the lid's cap and put a towel over it to keep it from exploding the top off). Strain and chill. OR pour it into a container and let the flavors infuse for a day or two, then strain.