In so far as drinking water is concerned it is not important to know the hardness apart from the quantity and kind of mineral matters contained. In other words, for potable purposes, the hardness of water per se is of no consequence. The effect of the mineral matters in solution upon the health and digestion are the principal things, in fact, the only things to be considered in so far as drinking purposes are concerned. For technical purposes, however, the matter is quite different. Here it is of the utmost importance to know the character of the dissolved mineral matter. If, for instance, water is to be used in a steam boiler, the rapidity with which it coats the tubes and sides of the boiler is a matter of grave consequence. Often the tubes of the boiler become so coated with the deposited mineral matters as to make it almost impossible to generate steam therein. The boilers are rapidly burned out, great damage is caused, and danger of explosion engendered.

Wherever water is to be used for technical purposes, it should be carefully examined, especially for its temporary hardness. Salts which are very soluble, such as the chlorids of soda, lime and magnesia, are of little consequence, but those which are easily precipitated, like the carbonates, sulphates, etc., are of great consequence. In such cases complete chemical analysis would be required to determine whether or not a water is suitable for purposes of this kind.