Page:The New International Encyclopædia 1st ed. v. 20.djvu/429

WATER-WORKS. 359 WATER-WORKS. the source and iiiodu of huijply, tlic latter in- volving a choice Ijctweeu gravity and jjuniping; the size and character of iiuniping works, reser- voirs, tanks, and standpipes ; the distribution system; and various details of public policy. Quality, or the litness of water for its vari- ous usesj includes freedom from the specific germs of disease and from minor substances dele- teri(nis to health, an absence of turbidity and color, uniileasant taste or odors, and of all min- eral matters in sufficient quantities to interfere with the various household and industrial pur- poses for which the water is designed. The most serious menace to watcn- supplies is seiaiiin pol- hitioii, which may at any time cause an epiilemic of typhoid fever and is likewise one of the chief agents in the spread of cholera. In addition, sewage pollution may give rise to various troubles of the digestive tract and render the sj-stem less able to resist various tendencies to ill health and disease. fiedimcnlury matter, otherwise known as muddiness or turbidity, is generally caused by clay and silt suspended in the water. It is more offensive than dangerous, but may prove harmful if taken into the system frequently or in large quantities. Color is still more wholly a matter of offensiveness to the eye, instead of a menace to health, than is sediment. The latter gives rise to an apparent color, which disajipears with the sediment. True color, as used in water terminology', is generally a stain, rather than matter in suspension, it is fre- quentl}- due to infusions of vegetable organic matter, like leaves, grass, and peat. Odor, in any considerable degree, is less frequent and far more troublesome than either sediment or color. It is commonly due to the life processes of minute organisms in the water and is fre- quently seasonal in its appearance. Sediment, odor, and taste, as well as the evil effects of sewage pollution, each yield to proper treatment, as described luider Water Purification. Water Analy.ses and Their Interpretation. As an aid to the study of the quality of water recourse is had to an inspection of the drainage area and all possible sources of pollution, and to physical, chemical, and biological examina- tions of samples of the water. The physical ex- aminations involve observations on temperature, color, odor, and turbidity. Color is generally determined b,v comparing the samples of water with fixed color standards based on chemical so- lutions of known composition and regularly varj'- ing strength. The most commonl.v accepted measure of turbidity is the dejith at which some bright object will disappear from view if gradu- all.v lowered in water. High temperatures give rise to troublesome organic growths. As a rule, however, temperatures are quite beyond control, except in choosing between different sources of suppl.v and in locating the depths of the pipes through which water is drawn from deep lakes and reservoirs. Deep temperature readings are taken by means of the thermophone. Absence of color, odor, and turbidity, combined with low temperatures, are most desirable qualities, but all of them together are of vastly less im- portance than freedom from organic impurities. Unfortunately, no method of analysis has been discovered which will do more than indicate the probable safety or danger of a given water. Chemical analyses point to past contamination, and give some evidence of its nearness or dis- tance in point of time and whether it was of animal or vegetable origin. Bacterial analy.ses are of comparatively little avail except to show the numbers of bacteria present, and to throw some light on their prob- able origin. The dillerentialion of the typhoid germ, the cliief object of fear in America", from the luirndess water bacteria is a long, tedicjus, and at best a very uncertain operation. The more direct microscopical examinations of forms of life above the bacteria, although of much future promise, is limited chiefly to determining the absence or occurrence of those growths that cause bad tastes and cxlors. But when such growths are detected the most that can be done, ordinarily, is to shut off the water in question, take stejjs for its purification, or exclude light, when the latter is an essential to troublesome visitors. As an aid to detecting organic im- purities, chemical determinations of albumi- noid and free ammonia, nitrates, and clilurine are made. The first four substances indicate past contamination. Their relative amounts, in the order named, throu- some light upon the degree of natural ])urification, as measured chem- icallj', that has taken place. The chlorine, if above the local normal for unpolluted water, in- dicates that the organic matter came from sew- age. High nitrates and clilorine combined, espe- cially if accomp.-inied by large numbers of bac- teria, render water very" suspicious. If, in addi- tion, CoH coitimiinis, a kind of bacteria found in large quantities in the human intestine, are present, the evidence against the water is often held to be conclusive. It may be accepted as quite so if it is learned that sewage is being discharged into the stream or lake above the point of inlet. See Disease, Germ Theory ok. Xo determinations of the mineral contents of water are made in the case of surface sui)plies unless they come from limestone regions and ex- cessive hardness is feared. Underground waters are so likely to contain the sulphates and car- bonates that cause hardness, or else other troublesome mineral salts, particularly iron com- pounds, that it may be well to test for at least those substances when examining well water. Lead poisoning is not due to lead normally in the water, but to lead taken up by the pas"sage of certain water through, and more particularly by its standing in, lead pipes or cisterns. Very soft waters are especially liable to attack lead pipe. Chemical standards for water are very mis- leading. The best chemists and engineers int'erpret each .set of analyses in the light of all other known facts and attempt to lay down no arbi- trary standards. A minimum of 100 to 500 bac- teria per cubic centimeter has been set by vari- ous authorities; but this, also, depends "on all the other local conditions. Hardness is chiefly a question of more or less soap in connection with water used for household purposes, and of scale formation in steam boilers. If excessive, the supply may be rejected, or a softening plant may be supplied. The substitution of pure mountain for contaminated Passaic Eiver water at Newark in 1S02, and of filtered for unfiltered water, at Lawrence. jMass., in 1893, and at Al- bany, N. Y., in 1899, are among the best Ameri- can exiyuples of the decline in t.vphoid mortality following upon improved water supplies.