Here's why:

* Natural Filtration: Spring water forms when rainwater percolates through underground rock formations. As it travels, it dissolves minerals from the rocks.

* Mineral Content Varies: The specific minerals present and their concentrations vary depending on the type of rock the water passes through. Some common minerals found in spring water include calcium, magnesium, potassium, sodium, and bicarbonate.

* "Mineral Water" vs. "Spring Water": "Mineral water" is a specific type of spring water that has a significant mineral content (typically more than 250 milligrams per liter of dissolved solids).

Note: While some mineral content is natural, some bottled spring water may have minerals added during processing.