In a large pot, bring 8 cups water to a boil over high heat.  Remove from heat and add tea bags.  Steep tea, covered, for about 5 minutes, then remove tea bags.

Mix in Truvia if you're using it.  Allow tea to cool.

Add lemon juice to tea.

In a small dish, heat blackberries in microwave for 15 seconds.  Mash the berries and mix in to tea.

Strain tea into a pitcher and add lemon slices and blackberries as a garnish if desired.

Top off with 2 cups of sparkling water and gently stir.