In a medium saucepan, combine the blueberries and 1 cup of water. Bring to a boil over medium heat, then reduce the heat and let it 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 down to extract as much liquid as possible. Discard the solids.

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 5 minutes.

Remove the tea bags and stir in the blueberry juice and sugar until the sugar is dissolved. Add the lemon juice and mix well.

Allow the mixture to cool to room temperature, then refrigerate for at least 1 hour to chill.

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