How do you decrease the calcium in well water?
Use an ion-exchange water softener. Check your local yellow pages.
Yes, clearly. A well has a source of water that collectively gathers over time. The water levels increase and decrease with time. Anything with a source such as water in a well can decrease to nothing. Since a well has a source, the source can become vacant and completely run out of water. This doesn't mean the well will be dry forever, just that it's possible.
Well . . . there are no calcium deposits in water, there is only calcium. The deposits happen on things that the water falls on, then dries. What is left is a deposit. To remove the calcium (and magnesium) from water, you run the water through a tank full of little beads of "Filtersord". Most water purifiers use this along with charcoal, which removes bits of dust, and so forth.
the parathyroid hormone (PTH) is released by the parathyroid gland (located behind the thyroid gland). A decrease in blood calcium causes the parathyroid gland to secrete PTH which causes the bones to release more calcium to raise blood calcium and also causes the kidneys to decrease the amount of calcium lost in urine
See http://www.fiu.edu/~pricer/Calcium%20Carbonate.pdf. The solubility of CaCO3 depends on the solubility of CO2. The solubility of gases decreases in water as the temperature rises. This behavior is discussed at http://antoine.frostburg.edu/chem/senese/101/solutions/faq/temperature-gas-solubility.shtml.