In a small saucepan, create a simple syrup by dissolving the sugar in 1 cup of water over medium heat. Once the sugar has dissolved, remove the saucepan from the heat.

Add the fresh basil leaves to the simple syrup and let them infuse for 10 minutes. Strain the basil leaves out, reserving the syrup.

In a large pitcher, combine the fresh lemon juice, the basil-infused simple syrup, and the remaining 5 cups of cold water. Stir well.

Taste and adjust sweetness if necessary. If using a natural sweetener like honey or agave syrup, gently warm it with water to combine before adding to the pitcher.

Add ice to the pitcher, and garnish with fresh basil leaves and lemon slices.

Serve the lemonade over ice, garnished with a sprig of basil and a slice of lemon in each glass.