To make the lemonade, prepare a simple syrup by heating 3 cups water and 3 cup sugar over medium heat. Cook until the sugar dissolves. Remove from heat and chill until ready to use.
Meanwhile mix lemon juice and remaining four cups of water and ice together in a large pitcher.
To make the tea, brew the tea by bringing 12 cups of water to a boil. Place 12 teabags in a pitcher and pour the water over the top. Let steep for 15 minutes. Remove teabags and discard.
Puree blackberries in a food processor strain though a fine mesh sieve to remove the seeds. Add puree and mint leaves to brewed tea. Mix well.
Add the cooled simple syrup to the lemon juice and water pitcher. Mix well. Pour in the blackberry tea. Mix well. Chill and serve.