1-1/4cupsfreshly squeezed lemon juice(from about 15 lemons), strained
In a small saucepan, combine the blueberries, sugar, rosemary, and 1/4 cup water over medium-low heat and simmer, stirring occasionally, until the blueberries are soft and broken down, about 10 minutes. Let cool.
Strain the blueberry syrup through a fine-mesh sieve into a pitcher, gently pressing down on the solids to extract the juice. Stir the lemon juice and 2 cups water into the pitcher. Add ice and serve.