Prepare a boiling water bath canner and 3 half pint jars.

Pour the juice into a low wide non-reactive pan that can hold at least five quarts (this jelly bubbles up a lot during cooking, so you need the room for expansion).

Bring the juice to a boil. Once it boils, add 1 cup granulated sugar and the tablespoon of calcium water and continue to boil for another five minutes.

Whisk the pectin powder into the remaining sugar.

Once the five minutes are up, slowly whisk the pectin-spiked sugar into the boiling juice. I do this with a whisk in one hand and the vessel with the pectin in the other, to ensure that the pectin gets integrated into the juice smoothly and doesn't clump.

Once the the pectin is fully integrated, boil for another minute and then remove the jelly from the heat.

Funnel the jelly into the prepared jars, leaving 1/4 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.