Sweet-tart sour mix made with fresh citrus juice, no food coloring or corn syrup added. I like pouring the finished mix into a Pyrex measuring cup so I know how much I have as I'm making cocktails, but a squirt bottle or plastic container with a lid works too.
Remove 1-2 thick strips of peel from each citrus fruit, being careful to just take the peel and leave the white pith behind, and set aside.
Juice each of the citrus fruits to yield approximately ½ cup orange juice, ¼ cup lemon juice, and ¼ cup lime juice.
Add the citrus peels to a small saucepan with the sugar, water, and citrus juices.
Heat until the sugar has melted, swirling or stirring the pan occasionally. Simmer mixture until reduced slightly (it will be thicker and syrupy), about 15-20 minutes. Let cool completely and store, covered, in the refrigerator until ready to use.