Wikipedia
Mineral springs are naturally occurring springs that produce water containing minerals, or other dissolved substances, that alter its taste or give it a purported therapeutic value. Salts, sulfur compounds, and gases are among the substances that can be dissolved in the spring water during its passage underground.
Mineral water obtained from mineral springs has long been an important commercial proposition.
Mineral spas are resorts that have developed around mineral springs, where (often wealthy) patrons would repair to “take the waters” — meaning that they would drink (see hydrotherapy and water cure) or bathe in (see balneotherapy) the mineral water.
Historical mineral springs were often outfitted with elaborate stone-works — including artificial pools, retaining walls, colonnades and roofs — sometimes in the form of fanciful "Greek temples", gazebos or pagodas. Others were entirely enclosed within spring houses.