Short answers, pulled from the story.
A spring is a natural exit point where groundwater from an aquifer emerges onto the surface as flowing water. Springs form when the water table rises above ground level, when terrain drops sharply, or when an impermeable rock layer forces groundwater sideways until it finds an outlet. Karst topography, volcanic activity, and artesian pressure can also produce springs.
A first-magnitude spring is one that discharges water at a rate of at least 2,800 liters, or 100 cubic feet, per second. Florida has at least 27 known first-magnitude springs; the Missouri and Arkansas Ozarks contain 10; and 11 more are located in the Thousand Springs area along the Snake River in Idaho.
Spring water picks up dissolved minerals as it moves through underground rock, measured as total dissolved solids (TDS). Mineral water is defined as containing at least 250 parts per million TDS. Depending on the geology, spring water can be carbonated, sulfurous, iron-rich, or in some cases contain arsenic above the World Health Organization's safe limit of 10 parts per billion.
Thermal springs are fed by geothermally heated groundwater, typically running between 45 and 50 degrees Celsius. They have been used for bathing and balneotherapy for thousands of years. In the 20th century, hot springs became a renewable energy source for heating buildings; the city of Beppu in Japan draws hot water from 2,217 spring well heads.
Pythia, the Oracle at Delphi and high priestess of the Temple of Apollo, delivered prophecies in a state of divine possession said to be induced by vapors rising from a fissure in the rock. Scholars believe those vapors were emitted from the Kerna spring at Delphi, making the spring a likely physical source of the oracular experience.
The Greek myth of Narcissus is set at a spring. Ovid described the site as an unmuddied spring with silvery, glittering waters untouched by shepherds, animals, or fallen branches. Narcissus fell in love with his own reflection in this still spring pool.