Not only is it desirable to have water purified to remove colors and suspended matters which offend the eye, though perhaps not strictly inimical to health, but also, and this is most important, it is desirable to have a water supply which does not threaten health. In nearly all cases of purification of water for municipalities the death rate of water-carried diseases, typical of which is typhoid fever, has decreased. In some instances this decrease has been most marked, while in others it has been slow and not so striking. The report of the Committee on Water Supplies of the American Public Health Association, for 1913, shows the following effect upon typhoid fever death rates for the following cities using mechanical and sand filters:

From the above tabulation it is apparent that mechanical filters are more effective than sand filters in diminishing the death rate from typhoid. Whether this is a mere coincidence, or whether it is based upon the essential and radical differences of the two methods, I am unable to say. Very often the good effect of filtration in the diminution of the typhoid death rate is not exhibited at once, but only after a number of years. This, I think, is probably due to the fact that the water pipes and distributing pipes of the cities often contain deposits which tend to retain the typhoid bacillus so that it may be constantly regenerated. Thus, it requires several years to remove the infection from the distributing system. It would be advisable, I think, in cases of this kind, to force through the distributing system water heavily charged with hypochlorite of lime or some other germicidal body, and allow it to flow freely from the spigots in every house. The residual water could then be driven out by the freshly filtered water for two or three days, until the germicide is eliminated.

An instance of the slow effect of diminishing typhoid death rate is seen in the case of the city of Washington, where the diminution of the death rate has been extremely slow. At this date (Jan. 1918) the morbidity of typhoid has been so greatly reduced that only 30 cases are under treatment. Another instance is that of New Orleans, where filtration was first established in 1909. The previous death rate per hundred thousand in New Orleans had ranged from 55 in 1907 to 29 in 1908. The first year after filtration the death rate remained at 29; in the second and third years it rose to 32 and 31 respectively; while in 1912 the effect of the filtration began to be distinctly felt, when the death rate fell to 14.

In general it may be said that the improvement of drainage, the establishment of efficient sewage systems, the installation of sanitary privies, and the purification of the water, have added very greatly to the average life of the inhabitants of our cities. But the full measure of benefit has not yet been accomplished. Many cities are expending vast sums of money in seeking unpolluted sources of water supply. Seattle, San Francisco and Los Angeles, on the Pacific Coast, have spent, or are to spend, hundreds of millions of dollars to secure a pure water supply from the mountains. New York City has just expended a vast sum to get its water supply from an uncontaminated source. In my opinion, no kind of a debt which promises more benefit to future generations can be contracted than that which looks to the sanitary betterment of the water supply.