Wash, stem, pit cherries. Chop either with a large French knife or in a food processor. Add to the large pot.
Add the calcium water and the apple juice to the pot, stir.
Add any sweetener, if using (optional. See Recipe Notes.)
Put pot on stove burner, and turn burner on to start heating the mixture in the pot.
Put the lemon juice in a bowl. Sprinkle the pectin powder over, all at once, and whisk till smooth (don't worry about very small lumps they will dissolve in the heat later.)
When the pot mixture hits a boil, add the pectin mixture a dollop at a time, stirring all the while.
When the pectin mixture is all in, let the mixture cook for 1 more minute.
Remove from heat.
Taste, and see if you want any sweetener in it; if so, add maybe ¼ teaspoon at a time of the liquid stevia or a tablespoon of honey at a time until it's right for your taste.
Ladle into 125 ml (4 oz) or quarter-litre (½ US pint / 8 oz) jars.
Leave 1 cm (¼ inch) headspace.
Debubble, then adjust headspace.
Wipe jar rims.
Put lids on.
Process in a water bath or steam canner.
Process for either size jars 10 minutes; increase time as needed for your altitude.