2 c water
2 c sugar
zest of 3 limes or 1 lemon
fresh lemon or lime juice (juice of about ten limes or lemons)

Put the water in a small pot. Stir the sugar and zest into the water. Boil for 5 minutes. Remove from heat. Add the freshly squeezed juice. Pour into a glass container and refrigerate.

To serve, put one part cordial and five parts cold water into a cold glass. Put a lime or lemon slice on the edge of the glass if you want to be fancy.