CHAPTER VII.

IMPURE WATER, AND ITS EFFECTS ON PUBLIC HEALTH.

ALTHOUGH impure water has long been recognised as one of the most potent causes of disease, it is only of recent years that minute investigation has succeeded in demonstrating the terrible morality which it inflicts on all classes of the community. It is true that chemical analysis often fails in detecting the special impurities on which the development of certain diseases depends ; it is also true that, even when impurities are detected, it is extremely difficult to estimate their exact etiological value; nevertheless, the broad fact remains, and it is founded on evidence of the most conclusive kind, that a large number of cases of disease are attributable to the use of impure water, and there are good grounds for believing that, as investigations become more frequent and precise, a continually increasing class of such cases will be discovered. It must also be remembered that the effects of impure water, like the effects of impure air, may engender a general impairment of the health, without giving rise to well-pronounced disease.

Water impurities and their effects may be conveniently considered as follows:-Firstly, water rendered impure by an excess of mineral substances; secondly, water rendered impure by the presence of vegetable matter; thirdly, water rendered impure by animal organic matter.

SECTION I.-WATER RENDERED IMPURE BY AN EXCESS OF MINERAL SUBSTANCES.

As all potable waters contain a certain amount of mineral matters, it is extremely difficult to decide the quantities of these ingredients which may be present, either singly or collectively, without producing bad effects. This much, however, may be said, that waters of a moderate amount of hardness, provided that the hardness depends chiefly on the presence of calcium carbonate, are not found to be detrimental to health. A water of 8 or 10 degrees of temporary hardness, equivalent to about as many grains per gallon of total mineral solids, may be pronounced good and wholesome, while one of as many degrees of permanent hardness would prove injurious to many persons. With regard

to the wholesomeness of Thames water, with a hardness averaging 15 degrees before boiling and 5 degrees after, the evidence given before the Royal Commission on Water Supply, 1869, is somewhat conflicting; for while Dr. Letheby considered a moderately hard water, such as the Thames water, best suited for drinking purposes and the supply of cities, Dr. Parkes maintained that the amount of hardness should not exceed 10 or 12 degrees if possible. Mr. Simon and Dr. Lyon Playfair, on the other hand, although they did not condemn the London water on account of its hardness, both expressed themselves in favour of a softer water for purposes of health. The inference that may be drawn from this and other evidence would therefore appear to be this, that the total hardness of a water ought not to exceed 15 degrees, nor the permanent hardness 5; or, in other words, that even in a moderately hard water, calcium

carbonate must always greatly exceed the magnesium and calcium sulphates and sodium chloride.

The symptoms referable to an excess of hardness, arising from the presence of earthy salts, are mainly of a dyspeptic nature. According to Dr. Sutherland, the use of the hard waters derived from the red sandstone rocks underlying Liverpool, produced, in many cases, constipation and visceral obstruction, and an excess of calcium and magnesium sulphates (7 to 10 grains per gallon) has been known to produce diarrhoea.

The special disease, however, which, more than any other, seems intimately connected with the mineral ingredients of water, is goïtre. In Nottingham, where the disease prevails to a certain extent, the common people attribute it to the hardness of the water; and in other parts of England, such as Yorkshire, Derbyshire, Hampshire, and Sussex, it is found to prevail only in those districts where the magnesian limestone formation abounds. According to Dr. Coindet of Geneva, the disease is speedily produced in persons drinking the hard pump water in the lower streets of that town, while in other parts of Switzerland the use of spring water has been followed by the production or augmentation of the disease in a few days. In India, again, the researches, more especially of Dr. M'Clellan, show very conclusively that it is found to prevail only where the magnesian limestone formation prevails. Whether lime and magnesian salts, or ferrum sulphide, as has been suggested by M. Saint-Lager, be the active agents in producing the disease, has not yet been rendered quite clear; but it appears certain that goïtre is originated by water-impurities, and that these are of an inorganic and not organic nature. According to Johnston,

the prisoners in Durham jail were at one time affected with swellings of the neck, and on analysis the watersupply was found to contain 77 grains of lime and magnesian salts per gallon. The swellings disappeared when a purer water was obtained. (Parkes.)

The effects of minute traces of metallic compounds in drinking water are as yet comparatively unknown. It is quite possible that the sanitary condition of a district may in a great measure depend on impurities of this description, and, as Mr. Wanklyn suggests, that the salutary effect of "change of air" may be partly due to change in the minute metallic impurity in the water of the parts of the country which are visited.

Of the metallic ingredients, the effects of iron and lead have been the most fully ascertained. It would appear that iron, if present in quantities large enough to impart a chalybeate taste to the water, often produces headache, slight dyspepsia, and general mal-aise, while impregnation with lead from leaden cisterns or pipes has frequently been followed by symptoms of lead-poisoning. In the case of the ex-royal family of France, many of whom suffered when at Claremont from this species of water-contamination, the amount did not exceed one grain per gallon; indeed, from cases which have since occurred, it seems probable that the habitual use of water containing from one-tenth to one-twentieth of a grain per gallon may be attended with danger. In his investigations with regard to the Devonshire colic, which formerly prevailed to a great extent, Sir George Baker found that eighteen bottles of cider which he examined contained 4 grains of lead, or a quarter of a grain to each bottle. The impregnation arose from lead being employed in the construction of the cider troughs. With

regard to the minor effects of lead-poisoning, Dr. B. W. Richardson remarks that "contamination of water, both hard and soft, impure and pure, by lead, is, in all parts of the kingdom and under every variety of circumstances, the cause or source of various obscure diseases of man (and also, doubtless, of the lower animals), of the nature specially of dyspepsia and colic. This proposition was abundantly proved by cases of minor diseases induced by lead-contamination of various of the hard or impure waters of London."

Arsenic, copper, or mercury, are only found in the drinking waters of this country in injurious quantities when streams are polluted by the washings from mines or chemical works.

SECTION II.-WATER RENDERED IMPURE BY

VEGETABLE MATTER.

Vegetable matter may be present in water either in suspension or in solution. In peaty water, which is characterised by its brownish tint, the dissolved impurities sometimes do not exceed two grains per gallon. In the absence of a purer supply, a water of this description cannot be pronounced objectionable, provided that it is not stored in leaden cisterns, and that the supply is constant. If stored in open-air ponds or reservoirs, it is improved by oxidation and light; and it is further. improved by filtration through gravel and sand.

Water containing a considerable amount of vegetable matter, partly in suspension and partly in solution, is decidedly unwholesome. It has been known to produce violent outbreaks of diarrhoea, and, since the days of Hippocrates downwards, it has been popularly acknowledged to be productive of ague and other malarious