. Preventive medicine and hygiene. nd pressure, so that deep wells and artesian waters are frequently SOURCES OF WATER 807 unfit for domestic use on account of tlie large amount of inorganicimpurities which they contain, such as lime, iron, common salt, etc. The water that soaks into the soil finally rests upon an imperviousstratum. Such water, as a rule, does not exist in the ground as a river ^or lake, but occupies rather the spaces between the sandy particles, exceptin limestone formations. Ground water, therefore, in any quantity isfound, as a rule, in sandy, gravelly, or sandstone formati
. Preventive medicine and hygiene. nd pressure, so that deep wells and artesian waters are frequently SOURCES OF WATER 807 unfit for domestic use on account of tlie large amount of inorganicimpurities which they contain, such as lime, iron, common salt, etc. The water that soaks into the soil finally rests upon an imperviousstratum. Such water, as a rule, does not exist in the ground as a river ^or lake, but occupies rather the spaces between the sandy particles, exceptin limestone formations. Ground water, therefore, in any quantity isfound, as a rule, in sandy, gravelly, or sandstone formations. All water finally reaches a certain level, where it ceases to pass,downward, and is then directed in a horizontal plane, forming a moreor less continuous bed of water. This is known as the ground-watertable, which underlies practically all the earths surface. It is tappedwhen wells are sunk, and forms springs, lakes and marshes, where itreaches the surface. It is only in limestone regions that the ground water exists as flow-. FiG. 97.—Ground Water. A. High level. B. Low level. C. Intermittent spring. ing rivers or in large bodies. In such instances, as, for example, themammoth cave in Kentucky, the underground river may appear anddisappear suddenly. The sanitary significance of water from limestonecrevices is entirely different from that obtained from a sandy soil. The surface of the ground water does not follow the surface of theland, but more approximately the contour of the impervious stratum onwhich it rests. It crops out at the surface here and there, to form rivers,ponds, lakes, and springs. The irregularity of the surface of the groundwater table is due to a certain extent to the rainfall. During droughtthe level becomes more and more uniform, until it may become quitehorizontal. Movement.—In most cases, except where water lies in deep depres-sions and pockets, the ground water is in constant lateral motion. Thismotion is usually in the direction of outfall, th
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Keywords: ., bookauthorwh, bookcentury1900, bookdecade1910, booksubjecthygiene
