In a saucepan, combine water, frozen blueberries, lemon juice (and why not toss in the entire half of lemon), mint leaves, and maple syrup.
Place in a jar and allow to cool in the refrigerator.
Bring to a boil, reduce heat, and simmer for 20 minutes.
Remove from heat and strain through a fine mesh strainer into a large bowl. Using a spatula, press the blueberries into the strainer, releasing any juices.
Return the warm, strained liquid to the saucepan. Bring to a boil once again, reduce heat and simmer for about 20-30 minutes, until syrup is reduced to 2 cups of liquid.
To make blueberry soda, add a few tablespoons of blueberry syrup to iced soda water. Enjoy!