Mix the sugar and water in a wide-mouth, half-gallon Mason jar or a glass pitcher.
Rinse the peels and add them to the jar.
Put a lid on the Mason jar fitted with an airlock (you can buy them online) or use a regular lid. if using a pitcher, cover with plastic wrap.
Let the mixture sit at room temperature for three to seven days. Check it each day, and if you’re using a regular lid, open it to release any pressure.
It’s ready when you see small bubbles rising to the surface and some sticking to the side of the glass. Give it a taste test – it should be fizzy and sweet. Don’t wait too long or it will turn to vinegar.
Once it’s ready, strain into jars or bottles and refrigerate.
Serve it cold, with ice and seltzer if you like, and garnish with a lime or a sprinkle of cinnamon.