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

Strain Juice: Place a fine-mesh strainer or cheesecloth over a bowl. Pour rhubarb mixture through and let it drain naturally (don’t press it down or the jelly may turn cloudy). You should end up with about 3 cups of juice.

Prepare Jelly: Return the strained juice to a clean saucepan. Add lemon juice and pectin. Stir well and bring to a full rolling boil over high heat.

Add Sugar: Add all the sugar at once, stir to dissolve, and return to a rolling boil. Boil hard for 1–2 minutes, stirring constantly.

Test & Jar: Remove from heat and skim off any foam. Ladle hot jelly into sterilized jars, leaving 1/4-inch headspace. Wipe rims, seal with lids and bands.

Process (Optional): For longer storage, process jars in a boiling water bath for 10 minutes. Let cool undisturbed for 12–24 hours.