Sterilize five 8-ounce jars, keep hot. Prep lids and rings. Fill water bath canner and bring to boil.
In a small bowl, mix together sugar and pectin powder. Don’t skip this step, or your pectin will clump. Set aside.
In a large, non-reactive pot, combine mulberries, lemon juice and the calcium water. Bring to a full boil.
Add sugar-pectin mixture, stir mulberry jam vigorously 1-2 minutes while cooking to dissolve pectin. Return to boil and remove from heat.
Ladle mulberry jam into sterilized jars leaving 1/4″ headspace. Wipe rims clean and screw on the lids. Process for 10 minutes in water bath canner (add 1 minute for every 1,000 feet above sea level). Jam will last about three weeks once opened. Makes around 4-5 cups.