WATER SUPPLY.

FROM the earliest times an abundance of pure water has been regarded by mankind as one of the most desirable of blessings. When men, in the progress of civilization, began to mass themselves together in cities, one of the problems which early demanded consideration was, how to supply themselves with pure water.

There were various sources of supply-from wells, from streams, and from rain-water stored in cisterns. Some cities, like Rome, undertook gigantic hydraulic works, building magnificent aqueducts to conduct the water from distant sources of supply into the imperial city. Jerusalem constructed vast cisterns hewed out of the solid rock, and filled them by subterranean conduits leading outside the walls of the city. The great importance of pure drinking water as a factor in the preservation of health is becoming more and more recognized by scientists and medical men. It is now generally conceded that impurities in water are more potent in the origin and spread of disease than any other cause, and that the germs of many of the more fatal forms of disease are introduced into the system by means of water. Epidemics of zymotic disease, as typhoid fever and diphtheritis, have so frequently been proved to have arisen from the use of contaminated water, that there is no question as to its influence. This is abundantly shown in the fact that so soon as the cause is removed the disease has abated. It is true that this class of diseases arises from other causes, but the use of impure water is one of the most frequent. It is asserted by some writers who deny the connection between the use of polluted water and the increase of disease that water known to be very impure has been used for years with immunity from any zymotic disease. Although much has been said pro and con, it is undoubtedly true that the weight of evidence favors the theory that polluted water may, and does, become the cause of disease, and therefore the great importance which writers on sanitary science attach to the subject, and the importance of educating the public to right views and practices concerning their water supply.

SOURCES OF SUPPLY.

There are five sources of supply; namely, springs, streams and lakes, rain-water, and wells, each possessing different degrees of purity,

They are the natural drains of the territory through which they pass, receiving not only the rain-fall, but also all organic and inorganic matter washed into them by a thousand tributaries. After rains they become turbid with earth. They are the receptacles of all the waste products of the inhabitants of the district; they receive the contents of sewers, cess-pools and privies; the offal of distilleries, slaughterhouses and tanneries, and the refuse of factories. Into them are thrown carcasses of dead animals as the most expeditious method of burial. From swamps they receive the matter of vegetable decomposition, and are discolored by flowing over beds of peat. In the West the evil is not so serious on account of the low percentage of population to area, but some of our streams are beginning to show the effects of increasing population, and especially in the growth of towns of considerable size upon their banks. In the more densely populated districts of our Eastern States, and especially in parts of Europe, many of the streams are already hopelessly polluted, and the subject is eliciting the anxious consideration of sanitarians.

It is certain that until some method can be devised to utilize sewage, the offal and refuse of manufactories, slaughter-houses, and distilleries, streams must be the channels through which waste products may escape.

The objections to the use of the water of streams as a beverage are: the high temperature; its occasional turbid condition after excessive rains; and the great liability to contamination from organic matter and waste products of factories. From the difficulty of supplying large cities from any other source the question resolves itself into the problem of how to secure, under these unfavorable conditions, an adequate supply of wholesome water.

CHARACTERISTICS OF GOOD POTABLE WATER.

Absolutely pure water for domestic use is seldom to be obtained, and even if it could be, is hardly to be desired. Distilled water is unpalatable, having a flat, insipid taste. Indeed, water to be pleasant to the taste must contain in solution certain gases; and is not rendered unpalatable nor unwholesome by the admixture of mineral substances, unless these are in excessive quantity.

Waters which flow over or through granite and gneiss formations, are the purest, yet even these dissolve some mineral substances. The most common of these are the chlorides, sulphates, and carbonates of sodium, potassium, magnesium, and calcium, together with silica and

and of various degrees of abundance. In regard to purity they rank as follows:

Springs found in suitable localities, and furnishing an abundance of water, are very satisfactory sources of supply. Their advantages are a uniform temperature, and freedom from contamination. Their disadvantages are, their liability to contain in solution an objectionable quantity of substances; as iron, sulphur, salt, etc. When furnishing a large amount of water they can be used to supply numbers of families by conducting the water through pipes to the places of consumption.

Wells are of two kinds-deep and shallow. The first furnishes the purer water, to reach which it is generally necessary to bore through impervious clay. The water is, therefore, thoroughly filtrated in passing from the surface of the ground to the spot reached by the shaft. If too deep, however, as in the case of artesian wells, the water is liable to contain an exess of inorganic matter; as salts of magnesia and lime. Shallow wells, if favorably situated, usually furnish reasonably pure water; but unless care is taken in the selection of the site they will become polluted by organic matter, finding entrance by soil saturation, from surface drainage, or through fissures in the strata of the ground.

It would be commonly supposed that rain-water collected in clean cisterns from well washed roofs would fill all the conditions of purity and wholesomeness; and it would do so were it collected at a distance from towns and villages. But rain-water collected in towns is far from pure. The water in falling carries with it many gaseous and solid substances with which the atmosphere is loaded. Roofs of houses are covered with dust, excrement of birds, fungus growths; and it is impossible, without the most vigilant care, to prevent these impurities from being carried with the water into the cisterns in objectionable quantities. It is asserted, also, with good show of reason, that the softness of the water, though admirable for cleansing processes, unfits it for drinking purposes because the structures of the body are largely supplied from the mineral constituents of water.

Streams and lakes or ponds are placed last for several reasons.

aluminum. Iron is the metal most frequently found. To the presence of these minerals is due that quality of water called hardness. For cleansing purposes it is objectionable; but it is an open question, whether hard or soft water is most beneficial to health. Nearly all water contains, also in solution, more or less of vegetable organic matter, due to the action of water on the vegetable matter over which it flows, or to vegetable growths which live and die in the water itself. Water flowing through peat formation is often highly colored, but is not, on this account, considered unwholesome. It is well known that water of this character is often selected for ocean voyages, on account of its power of retaining its freshness for long periods. In England and Ireland, bog-water is held in high repute for its excellence. So it will be seen that water need by no means be pure to be considered potable. Many of the substances held in solution by water can hardly be regarded as impurities, and their presence, or absence, does not affect the health of the consumer. What, then, shall be regarded as constituting pollution of water?

As has been already remarked, it is difficult to find water entirely free from organic matters; and when these are present to only a slight extent, they do not affect to any appreciable degree the quality. If, however, the organic matter held in solution in water exceeds a certain proportion, it becomes injurious to health, and in still greater quantity, dangerous to life. Of organic matter, the first in point of virulence are the dejections from human sources; and the most virulent of all are those from persons sick with zymotic disease. It has been well established that these diseases are communicated from the dejections of the sick finding their way into the stomach of the well. That water polluted with excrementitious matter alone can originate these diseases has been a matter of controversy, but that water polluted with execrementitious matter from persons sick with certain forms of disease will induce the same diseases, is a fact well established.

It has been argued by high authority that the reason of danger from organic pollution is, not that organic matter is harmful in itself, but that it serves as points of attachment and propagation of germs of septic diseases, and wherever there is organic pollution there also is danger of the presence of zymotic germs.

Second in point of danger is pollution from offal of slaughter-houses, and the refuse of tanneries.