Yield: 4 x quarter-litre (1/2 US pint / 8 oz / 250 ml) jars
Add the calcium water to the blueberries and rhubarb. If using sugar or Splenda. add the lemon juice now. Otherwise, do not add it yet.
If using sugar or Splenda. put them in a bowl, add the pectin powder, and mix. If using a liquid sweetener such as honey or liquid stevia, put instead the lemon juice in a bowl, add the pectin powder all at once, and stir it into the lemon juice.
Put the fruit pot back on the burner and bring to the boil.
When the pot has come to a full boil, stir in the pectin mixture a dollop at a time. If using a liquid sweetener such as honey or liquid stevia, add that to the pot now too.
Boil for another minute.