Combine 1 cup sugar and 1 cup water in a pot. Heat to a simmer, stirring until sugar is dissolved. Peel 6 strips of lemon rind and 6 strips of lime rind with a vegetable peeler. Squeeze lemons to get 3⁄4 cup juice and limes to get 1⁄2 cup juice, and set aside. Add peels and 1 cup cold water to pot. Pour into a jug and refrigerate for 2 hours. Add the lemon juice and lime juice. Slice 1 lemon and 1 lime, and stir into the jug.
SERVE WITH crushed ice.