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 mint leaves. Let the simple syrup cool.
Blend the blueberries with 2 cups of water. Then add the remaining 2 cups of water, lime juice, salt, and ¼ cup simple syrup. Blend to mix.
Pass the limeade through a strainer as you pour it into a pitcher.