For the sour mix: Combine 3 cups water, the sugar and the lime, lemon and orange zests in a medium saucepan and bring to a boil over high heat. Cook until the sugar is completely melted. Remove from the heat and let steep in the refrigerator until very cold and the flavor has infused for at least 2 hours and up to 24 hours.
Strain the cold syrup into a pitcher and add the lemon and lime juices.
For the long island iced tea: Combine 2 cups of the sour mix, the gin, rum, tequila, triple sec, vodka and lemon, lime and orange slices in a pitcher. Refrigerate for at least 1 hour and up to 24 hours.
Serve in tall glasses over crushed ice with a splash of cola if desired