The lost‑time element is an important one, and at Washington this was the main reason for trying surface raking. It became necessary to increase the output of the filters, and the ordinary scraping consumed so much time that the sand‑handling force was increased, working day and night. The raking expedient introduced at this time overcame this, and Mr. Hardy states that it is still followed when the work is at all pressing. The speaker has found at Pittsburg, as Mr. Hardy has found at Washington, that raking is nearly if not quite as effective as scraping in restoring the filter capacity.
Eleven years ago the speaker was connected with the preliminary investigations into the best methods of purifying the Potomac River water for Washington. It then appeared that while for the greater part of the time during an average year the Potomac River could be classed among the clear waters of the East, there were periods when excessive turbidity made it necessary to consider carefully methods of preparatory treatment before this water could be filtered effectively and economically. As Mr. Hardy has said, considerable prejudice existed against the use of a coagulating chemical, and the expedient was therefore adopted of giving the water a long period of sedimentation in order to remove enough of the suspended matter to allow the clarified water to be treated on slow sand filters. The expert commission, consisting of Messrs. Hering, Fuller, and Hazen, recommended the occasional use of a coagulating chemical, but this recommendation was not carried out.
The Potomac River is somewhat peculiar, in that the turbidity of its waters, as shown by the results presented in Mr. Hardy's paper, ranges from 3,000 to practically nothing. The bacterial content also varies widely, and Mr. Hardy's tables show this variation to be from 76,000 to 325 per cu. cm. Such a water as this requires particularly careful preparatory treatment. The Dalecarlia Reservoir has a capacity of something like 2 days' storage, the Georgetown Reservoir the same, and the McMillan Park Reservoir nearly 3 days, making a total sedimentation of more than 7 days. Without the use of a coagulant, it is significant that during a period of five years, even with 7 days' sedimentation, the average maximum turbidity of the water delivered to the filters was 106 parts per million, and the maximum average turbidity in one month was 250 parts per million. The water filtration engineer can readily understand that waters as turbid as this cannot be treated economically and efficiently in slow sand filters. It would appear that coagulating works might advantageously have been installed at the entrance to the Dalecarlia Reservoir. If this had been done, and coagulant had been added to the water at times when it was excessively turbid, a considerably shorter period of subsequent sedimentation than now exists would in all probability have rendered the water at all times amenable to efficient and economical slow sand filter treatment.
The prejudice in Washington against the use of coagulants has also manifested itself in other localities, but the results which have been obtained during the past twenty years from rapid sand filters and from slow sand filters, treating waters previously coagulated with salts of iron or alumina, have shown how thoroughly unreasonable were these objections. In this connection it is interesting to note that there are in the United States more than 350 rapid sand filter plants, and that nearly 12% of the urban population of Continental United States is being supplied with water filtered through rapid sand filters, in connection with all of which a coagulating chemical is used in the preparatory treatment.
| Note.— | Statistics from Birmingham, Ala., Dayton, Ohio, Fall River, Mass., Louisville, Ky., Memphis, Tenn., Oakland, Cal., and Providence, R. I., are not included, as they are incomplete. |
|---|
| City. | Typhoid Fever Death Rate per 100,000 Population. | |||||||
|---|---|---|---|---|---|---|---|---|
| 1906 | 1907 | 1908 | 1909 | 1910 | Average for six years, 1900-05, inclusive. | Average for five years, 1906-10, inclusive. | Average for 11 years, 1900-11, inclusive. | |
| Albany, N. Y. | 20 | 20 | 11 | 19 | 15 | 25 | 17 | 21 |
| Atlanta, Ga. | 50 | 64 | 47 | 44 | 43 | 65 | 50 | 58 |
| Baltimore, Md. | 34 | 41 | 31 | 23 | 41 | 36 | 34 | 35 |
| Boston, Mass. | 22 | 10 | 26 | 14 | 11 | 23 | 16 | 20 |
| Bridgeport, Conn. | 10 | 13 | 13 | 13 | 9 | 15 | 12 | 14 |
| Buffalo, N. Y. | 24 | 29 | 21 | 23 | 20 | 29 | 23 | 26 |
| Cambridge, Mass. | 18 | 10 | 10 | 9 | 12 | 18 | 12 | 15 |
| Chicago, Ill. | 18 | 18 | 15 | 12 | 14 | 27 | 16 | 22 |
| Cincinnati, Ohio | 71 | 46 | 19 | 13 | 6 | 54 | 31 | 44 |
| Cleveland, Ohio | 20 | 19 | 13 | 12 | 19 | 51 | 17 | 36 |
| Columbus, Ohio | 45 | 38 | 110 | 17 | 13 | 61 | 45 | 54 |
| Denver, Colo. | 68 | 67 | 58 | 24 | 30 | 37 | 49 | 42 |
| Detroit, Mich. | 22 | 28 | 22 | 19 | 16 | 17 | 22 | 19 |
| Grand Rapids, Mich. | 39 | 30 | 30 | 17 | 27 | 34 | 28 | 31 |
| Indianapolis, Ind. | 39 | 29 | 26 | 22 | 31 | 76 | 30 | 55 |
| Jersey City, N. J. | 20 | 14 | 10 | 8 | 10 | 19 | 12 | 16 |
| Kansas City, Mo. | 38 | 40 | 35 | 23 | 38 | 48 | 35 | 42 |
| Los Angeles, Cal. | 18 | 23 | 19 | 18 | 12 | 35 | 18 | 27 |
| Lowell, Mass. | 7 | 9 | 24 | 11 | 21 | 19 | 14 | 17 |
| Milwaukee, Wis. | 31 | 26 | 17 | 21 | 45 | 19 | 28 | 23 |
| Minneapolis, Minn. | 33 | 26 | 18 | 20 | 58 | 38 | 29 | 34 |
| Nashville, Tenn. | 66 | 85 | 62 | 53 | 48 | 54 | 58 | 56 |
| Newark, N. J. | 18 | 24 | 12 | 11 | 13 | 17 | 16 | 17 |
| New Haven, Conn. | 54 | 30 | 34 | 20 | 17 | 44 | 31 | 38 |
| New York, N. Y. | 15 | 17 | 12 | 12 | 12 | 19 | 14 | 17 |
| New Orleans, La. | 30 | 56 | 31 | 25 | 28 | 40 | 34 | 37 |
| Omaha, Nebr. | 28 | 24 | 22 | 31 | 75 | 20 | 36 | 27 |
| Paterson, N. J. | 4 | 11 | 10 | 5 | 7 | 25 | 7 | 17 |
| Philadelphia, Pa. | 74 | 60 | 36 | 22 | 17 | 47 | 42 | 45 |
| Pittsburg, Pa. | 141 | 135 | 53[1] | 13[1] | 12[1] | 132 | 71 | 104 |
| Richmond, Va. | 44 | 41 | 50 | 24 | 22 | 66 | 36 | 53 |
| Rochester, N. Y. | 17 | 16 | 12 | 9 | 13 | 15 | 13 | 14 |
| St Louis, Mo. | 18 | 16 | 15 | 15 | 14 | 33 | 16 | 25 |
| St Paul, Minn. | 21 | 17 | 12 | 20 | 20 | 14 | 18 | 16 |
| San Francisco, Cal. | ... | 57 | 27 | 17 | 15 | 20 | 29 | 24 |
| Scranton, Pa. | 11 | 76 | 11 | 11 | 14 | 18 | 35 | 26 |
| Syracuse, N. Y. | 10 | 16 | 15 | 12 | 30 | 14 | 17 | 15 |
| Toledo, Ohio | 45 | 36 | 40 | 31 | 32 | 36 | 37 | 36 |
| Worcester, Mass. | 12 | 14 | 10 | 8 | 16 | 17 | 12 | 15 |
| Washington, D. C. | 52 | 36 | 39 | 33 | 23 | 59 | 37 | 49 |
[1 Filtered water section. Allegheny District not included.]
Attention has repeatedly been called to the fact that the relatively high typhoid death rate in Washington, since the filter plant was installed, was a possible indication that the filters were inefficient. It is true that there has not been the marked reduction in the typhoid death rate in Washington, following the installation of the water filtration works, that has been observed in other cities in America. For the six years prior to the date on which filtered water was supplied to the citizens of Washington, the average typhoid fever death rate was 59 per 100,000 population, as against 37 per 100,000 for the five years following, a reduction of 37 per cent. At Albany, N. Y., where the first modern slow sand filter was built in 1899, the typhoid death rate has been reduced by 75 per cent. At Cincinnati, Ohio, the average death rate from typhoid ranged around 50 per 100,000 for years, but since the installation of the filtration plant it has been reduced to a point which places that city, with respect to freedom from typhoid fever, at the head of all the large cities in America; in 1910 the death rate from typhoid in Cincinnati was 6 per 100,000. Similarly, at Columbus, Ohio, where the typhoid death rate before the installation of the filtration plant in 1906 was even higher than at Cincinnati, it was reduced to less than 13 per 100,000 in 1910, whereas, for the previous five years, it was 61 per 100,000. Philadelphia, before the installation of the filtration works, had a typhoid death rate of 60 or more per 100,000, and in 1910 the death rate from this disease was 17. Pittsburg, at least that part of it now supplied with filtered water, for years had a typhoid death rate of more than 130 per 100,000, but the present rate is about 12 per 100,000.
While it may perhaps seem unreasonable to single out Washington as a particular sufferer in this respect, it is highly probable that a large share of the typhoid is still caused by secondary infection, flies, impure milk, and private and public wells. The speaker remembers distinctly that ten years ago, when he made an investigation into the purity of the water of about 100 public wells in that city, a large number of them showed unmistakable evidence of being polluted with sewagic matter. Conclusive evidence would be secured to dispel any doubt as to the sanitary quality of the filtered product if hypochlorite of lime were added to the filtered water throughout one year or throughout the typhoid months. It seems strange to the speaker, that for this, if for no other reason, this safe and non‑injurious germicide has not as yet been used at Washington, in view of the fact that at the present time it is being used continuously or intermittently in the treatment of the water supplies of scores of the most important cities of this country, among which may be mentioned New York, Philadelphia, Cincinnati, Pittsburg, St. Louis, and Minneapolis.