In a cocktail shaker with ice, add all ingredient except cola. Pour into a tall glass and top with cola. Garnish with a lemon wedge, optional.
For the sour mix- combine water and sugar in a small saucepan over medium heat. Stir until sugar dissolves. Bring to a simmer for 1-2 minutes. Let cool. Add lemon and lime juice. Pour into an air tight container and keep refrigerated for up to 2-3 weeks