“There are two distinct causes (each imparting to the water an odor and taste peculiar to itself) that have affected our reservoirs, at different periods, during the last few years: the one giving to the water the odor and taste of fish, the other imparting to it a musty odor and taste sometimes detected in dead wood. In the former, it is extremely difficult to satisfy consumers that the impurities are not due solely to fish in the reservoir, while in the latter they are equally confident that the reservoirs are little less than stagnant ponds.” The latter is sometimes exceedingly offensive and similar to sulphuretted hydrogen gas. In 1875 he again reports: “That all impounded waters in this section of the country are liable to become impure; that while the impurities have been traced to lower forms of animal organisms, little is known of the condition that favor their growth; that the germs of the organism probably come from the atmosphere.” Chicago will be compelled to move her crib further into the lake, now two miles from shore, to get beyond the limits of the Chicago River sewage. St. Louis, like Cincinnati, has outgrown its water system (established in 1872 at a cost of five millions,) and is obliged to drink muddy water. Cleveland extended its aqueduct in 1872, 1¼ miles into the lake in order to escape shore water. Detroit, after considerable discussion, removed their source of supply three miles above the city, and constructed new works in preference to expending more money on the old works. Rochester, N. Y., expended 4½ millions for bringing the water of Hemlock Lake thirty miles to the city. Baltimore celebrated only last October the opening of their new aqueduct, conveying the waters of Gunpowder River 7 miles in distance, at a cost of over four millions. Indianapolis has been compelled to erect new works owing to the contamination of the present source. CHAPTER III. PURIFICATION OF WATERS. The Rivers Pollution Commission of 1874, says, as regards filtration: “No process has yet been devised for cleaning surface water once contaminated with sewage, so as to make it fit for drinking.” Others say it is not safe to trust to dilution, storage, agitation, or filtration for periods of time, for the complete removal from water of disease-producing elements whatever they may be. Dr. Frankland states: “I believe the noxious parts in sewage is that which is held in mechanical suspension, not held in solution. I would not say it is impossible to remove it, but no system of filtration will secure its removal. There are only two processes by which it can be effectually removed--one by boiling for a long time, and the other by distillation.” The methods adopted for filtration of water are: “1. Infiltration--by intercepting underground currents through natural formations of beds or banks of water-courses.