In a medium saucepan over medium heat combine all of the ingredients. Bring to a simmer and stir until sugar dissolves.
Remove from heat and steep for 1 hour.
Strain the mixture to remove the solids and store in a glass jar for up to 2 weeks in the refrigerator.
To make a soda combine 1-2 tablespoons of the grapefruit syrup with 12 oz. of seltzer water. Stir and enjoy.