In a large sauce pan, combine the rhubarb and about 3/4 cup water. Bring to a boil, and then turn down the heat to let the rhubarb simmer until tender and it begins to break apart.
Prepare your canning supplies. Bring the temperature of the glass jars up by processing them in hot water for several minutes, and heat a few cups of water in a small saucepan for the lids. Stir in the pectin until dissolved. Bring back to a boil, and then add in the sugar all at once. Boil hard for a minute longer.
Skim off any foam and ladle the hot jam into the hot jars, leaving 1/4″ headspace. Place the lids and bands on top, screwing on the bands just until fingertip-tight. Place the full jars back into the boiling water and process 10 minutes.
Remove from the water and place the jars on a towel. Let the jars cool. The seals should suck down (you’ll hear a popping noise as they do). Makes about 5 eight-ounce jars.