Cook the rhubarb: In a large saucepan, combine chopped rhubarb and water. Bring to a boil, then reduce heat and simmer for about 10 minutes, or until the rhubarb is soft and breaking down.

Strain the juice: Pour the mixture through a fine mesh strainer or cheesecloth into a large bowl. Let it drain without pressing to keep the jelly clear. You should end up with about 3 to 3 ½ cups of juice.

Prepare jars and lids: While juice is straining, sterilize your jars and lids in boiling water or in a dishwasher with a sanitize cycle.

Make the jelly: Pour the rhubarb juice into a large clean saucepan. Add pectin and bring to a full rolling boil over high heat, stirring constantly.

Add sugar: Stir in the sugar all at once and return to a rolling boil. Boil hard for 1 minute, stirring constantly. Remove from heat and skim off any foam.

Fill the jars: Ladle hot jelly into prepared jars, leaving 1/4-inch headspace. Wipe rims clean, apply lids and screw bands until fingertip tight.

Process jars: Process in a boiling water bath for 10 minutes (adjust time for altitude if needed).

Cool and store: Remove jars, let them cool completely. Check seals after 24 hours. Store sealed jars in a cool, dark place.