In a large saucepan mix together the rhubarb, apples, sugar, water and cinnamon. Bring to a boil, then cook over medium heat for 20 minutes or until the fruit is soft. Stir in the pectin and boil for 5 minutes.
Ladle into sterile jars, wipe rims with a clean cloth or paper towel, and seal with new lids. Process in a bath of simmering water for at least 10 minutes, or as recommended by your local extension if you are at a high altitude. Store unopened jars in a cool dark place. Refrigerate jam after opening.
