Place the Tetley teabags in a large heatproof pitcher. Bring 6 cups of water to a simmer. Carefully pour the hot water into the pitcher, over the teabags. Allow to steep for about 5 to 10 minutes, depending on how strong you like your iced tea. Remove the teabags and discard. Let the tea cool down to room temperature. Place in the fridge, covered, and allow to chill for at least 1 hour.

Slice the watermelon in half and scoop out the flesh. Place it into a blender or food processor. Blend until completely smooth and juiced. Pour the watermelon juice through a fine-mesh strainer, into a large bowl or separate pitcher. Use a spoon to help pass the blended juice through the strainer. Discard the pulp and white seeds that are left behind. Cover and chill the watermelon juice.

Combine the ½ cup sugar and ½ cup water in a small sauce pot. Place over medium-high heat and bring to a simmer. Continue cooking until the sugar has completely dissolved. Remove from heat and stir in the sliced basil. Transfer to a glass measuring cup or other pouring vessel, and allow to cool down completely.

To make the iced tea, pour about 3 cups watermelon juice into the chilled tea. Add as much or as little of the basil simple syrup as you'd like, depending on how sweet you like your tea. Add the fresh lime juice and give it a big stir.

Serve with lots of ice in tall glasses. Garnish with a few lime slices, fresh basil leaves, and a slice of watermelon. Or use a melon baller to make watermelon rounds. Skewer two melon balls onto a toothpick and use as a garnish.

Will keep in the fridge, covered, for up to 4 days. If the tea has been sitting in the fridge, you'll notice that the watermelon juice and tea will separate, just give it a stir before serving! Enjoy!