Wash the rhubarb and cut away any bad spots. Cut it into slices that are about 1/2 inch in width. Measure out 1/2 cup of the sliced rhubarb and set it aside.
Take the rest of the rhubarb and place it into a pot. Add 2 cups of sugar and stir to combine. Tuck the hibiscus into a tea ball or a length of cheesecloth and nestle it into the rhubarb. Let it macerate for at least three hours and up to 24 (I did mine overnight).
When you're ready to cook, prepare a boiling water bath canner and four half pint jars.
Place the pot with the rhubarb on the stove over high heat, add the calcium water, and bring to a boil.
Cook, stirring regularly for 10 to 15 minutes, until the rhubarb starts to break down. If it's spitting, reduce the heat. Whisk the pectin powder into the remaining 2 tablespoons of sugar. Add this pectin-spiked sugar to the cooking jam in three stages, stirring well after each addition.
Finally, stir in the reserved rhubarb. Cook for an addition 1 to 2 minutes.
Remove the pot from the heat and fish out the hibiscus bundle or tea ball.
Funnel the finished jam into the prepared jars, leaving 1/2 inch headspace.
Wipe the rims, apply the lids and rings, and process in a boiling water bath canner for 10 minutes.
When the time is up, remove the jars and set them on a folded kitchen towel to cool. When the jars have cooled enough that you can comfortably handle them, check the seals. Sealed jars can be stored at room temperature for up to a year. Any unsealed jars should be refrigerated and used promptly.