Bring 6 cups water to a boil in a saucepan. Remove from the heat and add the rosemary and a pinch of salt. Cover and steep, 30 minutes. Strain into a pitcher and cool to room temperature.
Stir the lemon juice, agave nectar and 2 cups cold water into the pitcher. Add more lemon juice or agave nectar to taste. Serve over ice with more rosemary and/or lemon slices, if desired.
Photograph by Yunhee Kim
Recipe courtesy of Marcela Valladolid for Food Network Magazine