The classification of mineral waters is a subject the consideration of which would require a separate book, as its discussion is beset with many difficulties. All that is necessary here is to indicate the principal divisions, to one or another of which the springs are assigned in a general way. First, the waters are characterized in regard to their temperatures as either thermal or non-thermal, the temperature in the analytical report indicating, in most cases, to which of these classes the springs belong. Secondly, certain gases are usually present in the water of most springs, and these springs are indicated by the terms carbonated, sulphuretted, carburetted, etc. They are also mentioned as chalybeate, alkaline, saline, calcic, silicious, or acid, according to their predominant or characteristic solid constituents, or by a combination of the terms when more than one is present in large quantity.

Brine springs and wells (with a few exceptions where they have been used for medicinal purposes) have been omitted, as they are generally utilized in the production and manufacture of salt, and are therefore not usually applied to the ordinary uses of mineral springs.

Mineral waters owe their medicinal properties to the substances they contain in solution, derived from the soil or rocks through which they have passed in rising to the surface of the earth. These substances are chiefly soda, magnesia, lime, iron, and sulphur, and the acids combined with them are the muriatic, sulphuric, and carbonic. Thus the muriatic acid, united with soda, magnesia and lime, will give origin to the compound salts, muriate of soda, muriate of magnesia, and muriate of lime, and distinguish the group of mineral waters known as the muriated saline waters. In like manner, the sulphuric acid will give rise to sulphates of soda, magnesia, and lime, and constitute a group of sulphated saline waters, and the carbonic acid with similar bases will form carbonates of soda, magnesia, and lime, and compose a third group of carbonated saline, or, more correctly, carbonated alkaline waters. Iron is the basis of the chalybeate waters, and, to be held in solution, requires in the first instance to be united with oxygen, forming an oxide of iron, and it is rendered additionally soluble and efficacious by a combination of the oxide of iron with carbonic acid gas, constituting a carbonated or acidulated chalybeate water. Sulphur, forming the peculiar characteristic of the sulphurous waters, is present in the shape of sulphuretted hydrogen, and may be combined either with the muriated saline water, constituting a sulphuretted saline water, or with the carbonated saline water, so as to produce a sulphuretted alkaline water. In addition to the above, the presence of bromine and iodine in the waters gives rise to a bromated and Mated saline water; while certain waters are met with which are so deficient in salts of any kind, as to deserve the distinguishing title of negative waters.