From the American Journal of Clinical Nutrition:
Background: Calcium intake in North America remains substantially below recommended amounts. Bottled waters high in calcium could help close that gap.
Objectives: The objectives were to summarize and integrate published absorbability and biodynamic data concerning high-calcium mineral waters and to combine these data with hitherto unpublished analyses from my laboratory.
Design: The usual library database was searched. The absorbability of calcium from a high-mineral water labeled with tracer quantities of 45Ca was measured in human volunteers as a part of an otherwise low-calcium test meal. Published reports that used differing load sizes and meal conditions were harmonized by making corrections based on published calcium absorbability data.
Results: All the high-calcium mineral waters had absorbabilities equal to milk calcium or slightly better. When tested, all produced biodynamic responses indicative of absorption of appreciable quantities of calcium (ie, increased urinary calcium, decreased serum parathyroid hormone, decreased bone resorption biomarkers, and protection of bone mass).
Conclusion: High-calcium mineral waters could provide useful quantities of bioavailable calcium.