A pure water-supply has always been regarded as desirable and its value can hardly be overrated, from the standpoint of health, happiness, or economy. From the earliest history, no crime has been so despicable as that of deliberately poisoning a well from which the public supply was obtained, and in the past no charge more quickly could stir the populace to riot. In Strassburg in 1348 two thousand Jews were burned for this crime charged against them; and as late as 1832 the Parisian mob, frantic on account of the many deaths, insisted that the water-carriers who distributed water from the Seine, shockingly polluted with sewage as it was, had poisoned the water, and many of the carriers were murdered on this charge. Yet no water, as used for drinking purposes, is absolutely pure, according to the standards of chemistry. Distilled water is the nearest approach to pure water obtainable, and it is said by physicians that such water is not desirable as a habitual and constant beverage. The human body requires certain mineral salts particularly for the bones and muscles, and while these salts are provided in a large measure by food, a number are also furnished by drinking water. On the other hand, a wonderful natural process is accomplished by distilled or approximately pure water in that the water tends to dissolve, to add to itself, and to carry away whatever excess of solids may exist in the body. For certain kidney diseases, for example, pure water is prescribed, not merely as a means of preventing further accretions, but for the purpose of dissolving and removing the undesirable accumulations already existing. Practically, considerable latitude is possible in the matter of the purity of drinking water, and no particular harm is to be apprehended by the constant use of either a water containing as little as ten parts per million of total solids or of water containing as much as three hundred parts per million of total solids. The human body, in this as in so many other ways, is so constituted as to be able to adjust itself to varying conditions of food, and, until an excessive amount of ingredients are absorbed, no great harm is done. There are, however, certain definite substances--animal, vegetable, and mineral--which, when found in water, are decidedly objectionable, and it is not the amount of foreign matter in a water-supply, but its character, which is of importance in a water to be used for drinking. _Mineral matter in water._