Fun fact: The ancient Greeks wore rosemary garlands to boost their memory. Today, scientists believe it may protect your brain long-term.
In a small saucepan, combine 1 cup water and sugar. Bring to a boil, stirring occasionally to dissolve sugar. Remove from heat and add rosemary. Cover saucepan and let cool, about 2 hours.
Strain syrup into a pitcher. Stir in lemon juice and 3 cups cold water. Serve lemonade over ice.