In a medium saucepan, combine the blueberries and 1 cup of water. Bring to a boil over medium heat, then reduce the heat and simmer for about 10 minutes, mashing the blueberries with a spoon to release their juices.

Remove the saucepan from heat and strain the blueberry mixture through a fine mesh sieve into a bowl, pressing the solids to extract as much juice as possible. Discard the solids and set the blueberry juice aside.

In the same saucepan, bring the remaining 3 cups of water to a boil. Once boiling, remove from heat and add the tea bags. Let steep for about 5 minutes, then remove the tea bags.

Stir in the sugar while the tea is still warm until dissolved. Add the reserved blueberry juice and lemon juice, mixing well.

Allow the mixture to cool to room temperature, then refrigerate for at least 2 hours or until chilled.

Serve over ice and garnish with fresh mint leaves if desired.