Peel and chop prickly pear fruits.  Add them to a saucepan with enough water to cover.  Simmer for about 1 hour, adding more water to keep them covered.

Pour the fruit through a fine mesh strainer and measure the resulting juice.  You should have about 4 cups of juice from 8-10 fruits.

For every cup of juice, add 1/2 cup lemon juice and 1 cup sugar.  Reserve a small amount of sugar about 1/4 to 1/2 cup for mixing with the pectin powder. 

Add calcium water and bring the sugar/juice mixture to a boil.  Simmer for about 5 minutes.

Mix the pectin powder with the remaining sugar.  This is important because added on its own the pectin will clump instantly on contact with a liquid.  Stir in the pectin/sugar mixture and simmer for another 2 minutes.

Pour the prickly pear jelly into prepared canning jars, leaving 1/4 inch headspace.

Store jars in the refrigerator, or process in a water bath canner for 10 minutes.