If the water of a spring has gone deep enough into, or far enough through, the layers of the earth, it may, like water of some of the artesian wells, contain certain salts and minerals, particularly soda, sulphur, and iron.

Such springs are often highly valued as mineral water, healing springs, or baths, partly because of these salts, partly on account of their peculiar taste.

Most of the virtues ascribed to mineral waters or springs are due, however, to their _pure water_, and its cleansing effects internally and externally when freely used.
Springs are among the most highly prized sources of water supply, because they have gone underground sufficiently deep to become well filtered and cooled to a low temperature, and usually not far enough to become too heavily loaded with salts or minerals like the waters of the deep wells.

It must, however, be remembered that they also come from rain-water, and that in hilly or broken regions the source of that rain water may be the surface of the ground only a few hundred yards up the hill or mountain, and impurities there may affect it.

Much of the delightful sparkle of spring water is due, as in the case of the popular soda water, to the presence of carbon dioxid, only in spring water it is produced by the decomposition of vegetable matter in it.