In a medium saucepan, combine the blueberries, sugar & 1 cup of water. Bring to a boil, and smush the blueberries with a large wooden spoon. Reduce to medium and cook for 10 minutes. Pour the mixture through a sieve to remove the blueberries from the mixture. Pour the blueberry sugar liquid into a pitcher. Stir in the lemon juice & then stir in 7 cups of cold water.