To make a simple syrup, combine sugar, salt, and ½ cup water in a small pot. Bring to a boil. Stir, and reduce heat to medium high. Stir occasionally until sugar is dissolved, approximately 5 minutes.
Add the rosemary to the simple syrup. Let it cool.
Add 6 cups of water, lemon juice, and all of the simple syrup to a pitcher. Stir well, and chill.