I was drinking two to three gallons of liquids each day, maybe more, one summer while cycling the S-tier in the eastern regions, and hilly Texas farm roads. I must have lost quite a lot of calcium. I am not sure of any significant loss of bone density. I take supplements. The thing about calcium pills, they say, is that calcium from such sources may not be all that absorbable, ..........I definitely carry supplements with me on bicycling tours. My system may absorb only a percentage of the calcium in the tablet, but some is better than nothing at all.What greatly improves Calcium absorbtion from any source is Vitamin D and many, if not most of us, are deficient in it. We work indoors most of the time, and when we are outside we cover ourselves completely in high-SPF sunscreen. So, even being in sunlight doesn't develop the Vitamine D we need. A 2000 IU Vitamin D supliment taken daily is good insurance and really cheap if you buy house-brand or generics.