In a medium saucepan, combine frozen blueberries, water, raw sugar, and one tablespoon of fresh lemon juice. Heat over medium, bring to a boil, then reduce heat and simmer for 5 minutes.

Using a potato masher or immersion blender, gently crush the blueberries to release their juices fully, then strain through a fine sieve to separate the juice from the pulp.

In a separate pot, boil 6 cups of water and remove from heat. Add green tea bags or loose leaves; let steep for 3 minutes, then strain.

Mix the cooled blueberry juice and green tea in a large pitcher. Add remaining lemon juice, stir, and chill in the refrigerator for at least 30 minutes.