Wash red currants. Remove leaves. There is no need to remove the stems (aka "ribs"); you can just leave them on. In fact, many feel that the stems provide added pectin for a good set.
Place red currants and water in non-reactive saucepan.
Bring to a boil, then reduce to a simmer, covered, stirring occasionally and mashing gently every now and then until you have a pulp -- about 20 to 30 minutes. (Note: mash by hand, don't use a blender, food processor or anything mechanical as that will damage the pectin.)
Spoon into a jellybag or cloth to drain, suspended over a bowl. Let stand and drain for 2 to 4 hours, or overnight. When letting the juice drain, don't squeeze the bag or cloth to speed it up, or your jelly may well get cloudy.
This should yield somewhere in the range of 250 ml / 1 cup / 8 oz of juice per batch. If you don't get that, see notes below.
LIQUID SWEETENERS (HONEY, AGAVE, LIQUID STEVIA, ETC): See special directions below before proceeding further.
DRY SWEETENERS (SUGAR, SPLENDA, POWDERED STEVIA, ETC): Mix the pectin powder with the sugar in a small bowl or a measuring cup, set aside. Add the lemon juice and the calcium water to the pot. Bring pot contents to a boil, then add pectin mixture.
ALL SWEETENERS: When pot returns to a boil, let boil for 2 minutes, stirring constantly.
Skim surface scum off OR if desired strain again one last time through a jelly bag.
Ladle into 125 ml (4 oz) or quarter-litre (½ US pint / 8 oz) jars.
Leave 1 cm (¼ inch) headspace.
Debubble, adjust headspace if needed.
Wipe jar rims.
Put lids on.
Process in a water bath or steam canner.
Process jars for 10 minutes; increase time as needed for your altitude.