Bring 1 cup water to a boil in a medium saucepan. Add the sugar and stir until it dissolves. Add the strawberries and basil and continue to simmer for 5 minutes. Remove from the heat and let steep until completely cool. Strain the strawberry mixture and discard the solids.
In a 1-gallon container, add the lemon juice, 14 cups cold water and the strawberry basil syrup. Stir until well mixed. Pour the lemonade over a glass of ice, and top with a slice of lemon.