Mineral Water, water containing dissolved mineral salts. The mineral salts may occur naturally in the water or they may be added to it. Among the salts found in different mineral waters are various sodium, calcium, magnesium, and potassium compounds. Water containing calcium and magnesium is known as hard water; water that lacks these minerals is called soft water. In addition to mineral salts, many natural mineral waters contain gases, including carbon dioxide, hydrogen sulfide, and nitrogen.

Natural mineral water is groundwater that contains minerals dissolved from the underground rocks through which it passes. The water reaches the surface through wells or springs. Many hot springs, or thermal springs, yield water with a relatively high concentration of dissolved salts and gases. The water from such springs has been heated by hot or molten rock in the earth's crust, increasing its ability to dissolve other substances.

The bottling and selling of potable (drinkable) mineral water is a major industry worldwide. The concentration of mineral salts in different popular brands of mineral water varies, ranging from 500 ppm (parts per million) to more than 3,000 ppm. Bottled natural mineral water is typically named for the spring from which it is obtained. Sparkling mineral water is bottled mineral water that contains carbon dioxide gas. Some mineral waters are strong-smelling and bitter-tasting.

For centuries people have bathed at mineral springs to relieve the symptoms of skin diseases, arthritis, heart disorders, and respiratory infections. Springs used for this purpose—and the health resorts established at such springs—are commonly called spas. Patrons at medically supervised spas benefit from rest, good diet, light exercise, fresh air, and regular hours; whether the mineral content of the water provides any medical benefits has never been proven.