Layer the Ingredients. In a large pitcher, place the blackberries at the bottom. Add the thinly sliced lemon on top. If you're using mint, add it now for an extra layer of flavor.
Muddle gently. Using a muddler or the back of a spoon, gently press down on the blackberries and lemon slices. This helps to release their flavors. Be careful not to crush them completely.
Add Ice and water. Fill the pitcher with ice cubes to about halfway. Add cold water to fill the pitcher. Stir gently to combine all the ingredients.
Sweeten if desired. If you prefer a slightly sweeter drink, stir in honey or agave syrup to your taste.
Chill. Let the pitcher chill in the refrigerator for at least 1-2 hours. This allows the flavors to infuse thoroughly.
Serve. Pour the infused water into glasses, making sure each glass gets a few blackberries and lemon slices.