(Apologies, GoldStar, for a little detour here.)
Regarding the statement that we get most of our calcium from drinking water:
My recommended daily calcium intake is 1200 mg/day.
I get about 400 mg/day from food (estimated).
My drinking water has about 120 ppm calcium carbonate (=7 grains/gallon) per my water company.
How much tap water do I need to drink daily to make up that other 800 mg/day of calcium? I'd like to give up those chalky supplements.
My math skills are very rusty

, can anyone help me on this calculation? Thanks.