Since you are using the rinds, it is best if you use organic fruit.
Take 2-3 grapefruits and 2-3 lemons and remove the rinds.
Put rinds in a pot and cover with water about 3" above the peels.
Cover and simmer for 2-3 hours.
Leave lid on and let it cool.
Strain rinds out.
Sweeten with honey if desired.
Make in a large batch and freeze for future use