Prepare the blueberry syrup. Place water, sugar, and lemon zest in a small saucepan over medium heat. Stir occasionally until all the sugar dissolves. Bring to a simmer. Add blueberries. Lower the heat and simmer for 5 minutes. Strain the mixture and cool completely. Syrup can be kept in the refrigerator up to 5 days.
Prepare the lemonade. In a large pitcher, combine the water, lemon juice, blueberry syrup, sugar, and salt. Mix well until all the sugar is dissolved. Pour into ice-filled glasses. Garnish with lemon slices, blueberries, and mint.