Add 1/2 cup water and 1/2 cup granulated sugar to a medium saucepan over medium heat. Cook until sugar is completely dissolved. Remove from the heat and let cool to room temperature while you juice the citrus.
Transfer the simple syrup to a pint mason jar or other airtight container. Add 1/2 cup lemon juice and 1/2 cup lime juice. Cover and shake vigorously.
Store in the fridge until ready to use.
Notes
If you don’t want to spend the money on fresh-squeezed fruit juice (or you don’t have a neighbor with citrus trees), it’s totally okay to use the store-bought lemon and lime juice bottles.
Homemade sweet and sour mix will last 2 to 3 weeks in the refrigerator.
You can easily make larger or smaller batches following the 1:1:1:1 rule.