Measure jelly that needs to be rebatched. Wash and sanitize jars. Put jelly in a pot and bring to a boil.
In a bowl, mix sugar and pectin together to help the pectin not clump when you add to the jelly. Once the jelly boils stir in the pectin/sugar mixture. Add water and lemon juice and bring to a rolling boil over medium-high heat.
Stir constantly. Boil for 30 seconds and remove from heat. Skim any foam that formed on the top (optional).
Fill sanitized jars to 1/4 inch head space. Wipe the rims and put lids on. Rings should be finger-tip tight.
Process in a water bath canner for 5 minutes. Remove from canner and allow to cool for 12-24 hours. Check for proper seal and store in a cool, dry place with the rings off.