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It was contrary to expectation to find the number of bacteria greater on the surface than at points below. This is explained by the rapid current of the water passing from one reservoir into the other and out at the gate, thereby practically making a stream through the reservoir. The water evidently flows in the line of least resistance, and this is found at the surface. Consequently, the bulk of water passes through the reservoir in a surface current and allows the under straturn to deposit its bacteria. It also points to the fact that sedimentation does occur, but to a slight degree, especially so in those localities where the current is slackened or absent. It is not believed that the short time of three days would be sufficient to influence materially the number of bacteria. I am informed that the reservoir contains 150,850,000 gallons, which is a three days' supply for the city. Observations which were conducted with the London water supplyduring 1896 show that it requires at least ten days' storage before sedimentation diminishes the number of bacteria, and if the water was allowed to remain in storage for a month or more the sedimentation was more complete. The same conditions will apply to the public water supply. I am unable to state whether the Delecarlia and receiving reservoirs are of sufficient size to permit the storage of water for this length of time. There is an intimate relation existing between the number of bacteria present in a water supply and disease. Rivers or other sources of water supply which contain a large number of bacteria are responsible for the large number of diarrheal disorders. So if the number of bacteria is high and constant a water should always be looked upon with suspicion. A sudden rise in the number of bacteria in the Potomac water may not be of great importance, but the persistence of this large number is always to be regarded with suspicion. It is to be expected that a water supply receiving large quantities of decomposing organic matter—sewage, in other words—has associated with it a great number of bacteria. There is always a relative increase in the number of bacteria in river water during winter. This is due to two causes: First, increased washings from the soil; and second, the preservative action of low temperatures. It will be observed that during these months the typhoid-fever death rate is at its minimum, notwithstanding the increased number of micro-organisms. At first sight one might conclude that this would be a contradiction of the foregoing statement. The increase in the number of bacteria is synchronous with the increased volume, notably just after rains or during the winter months, when the precipitation is the heaviest. It would be natural to infer that if the number of bacteria were indicative of contamination there should be an increase in the number of diarrheal diseases. Yet this is not the rule. There are, however, exceptions. During the summer months there is an occasional heavy rain, which carries the sewage from the watershed to the river, and this rain is not sufficient to materially augment the body of water in the river. In this way it is probable that large quantities of concentrated sewage may suddenly be thrown into the water and do great harm. In the summer time the stream and tributaries receive a given quantity of sewage daily, the water becoming less in volume, thereby increasing the number of sewage bacteria many times over the number that are found in winter. While there is a relative increase in the number of bacteria during the winter months, there is also an increase in the volume of water, thereby dissipating in a measure the danger. This, I believe, is the explanation of why there is an increase in the number of cases of typhoid fever in the summer time over those of the winter. Now, if the river water would purify itself by means of aeration, light, and sedimentation, it should occur through the summer months, when the conditions are most favorable. We would expect a gradual diminution of sewage and colon groups of bacteria, and especially those contained in the Potomac River.

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The larger proportion of contamination of Potomac River occurs at and above Cumberland, Md. The tributary streams below this point do not add much to the contamination.

Mr. Newell, of the Geological Survey, states in his report that if we could dam off the stream below Cumberland, the greater part of the pollution would be removed. Now, if the river would purify itself by aeration and sedimentation, it would be natural to suppose that the pollution would become less and less as we approach Washington. On the contrary, Dr. Sprague reports that the samples of water taken at various places in the Potomac Basin do not show a diminution of the colon group, but a relative increase as we approach Washington. This fact alone would appear to be sufficient to demonstrate the fallacy of self-purification of a stream. There is evidently more than a coincidence between the presence of the colon group of bacteria and the number of cases of typhoid fever. Chart A has been prepared to show this relation.

By reference to this chart it will be seen that the upper line represents the total death rate, by months, from typhoid and typhomalarial fevers for the eleven years ending March 1, 1898. The second line represents the number of deaths from typhoid fever during this period, and the lower line the number of deaths from typhoid fever in the year 1897-98, ending March 1. There is no doubt that the deaths reported as typhomalarial are nothing more or less than typhoid, as the increase of deaths from this disease is synchronous with those of typhoid. By comparing these mortality curves with those prepared by Dr. Sprague in chart No. 1, it will be seen that there is a coincidence between these and the curve of the intestinal bacteria. The same relation between this group of bacteria and the prevalence of typhoid fever has been shown in cities other than Washington, as, for instance, Hamburg. Typhoid fever was endemic, prevailing in epidemic form in the summer and fall months. The bacteriological analysis of the drinking water demonstrated that the increased number of intestinal bacteria always coin. cided with the increased prevalence of typhoid fever and diarrheal diseases. This condition prevailed year after year until the water was filtered. Since then there have been no such coincidences.

We have still more evidences of the pollution of the Potomac River. Dr. Kober reports that in 1890 an epidemic of typhoid fever occurred in Cumberland, Md., and three weeks later there was an increase in the number of cases in Washington. If we allow from three to five days for a given volume of water to travel from Cumberland, Md., to Washington, and from fourteen to eighteen days for the period of incubation from typhoid fever, it would coincide with the increase in the number of cases.

The principal causes of pollution from sewage are derived from the towns and villages located in the Potomac Basin. There are about 35 of these located on the Potomac and its tributaries, which have in the aggregate a population of about 75,000, and are distributed as follows:

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Typhoid fever has been reported to prevail in Cumberland, Staunton, Harpers Ferry, Elk Garden, Westernport, Frederick, and Hagerstown.

The conclusion to be drawn from the above statements is that the Potomac is polluted with sewage to such an extent that it is a constant menace to the health of the inhabitants of the District of Columbia. This is not a new statement, but is made only to emphasize what is already well known.

REMEDY.

Several ways may be considered for purifying the water: First. The control of the watershed. Second. Seeking a new supply. Third. Improvement of the present supply. According to the report of the hydrographer of the Geological Survey, the drainage basin of the Potomac River has an area of over 11,000 square miles, which lies in four States—Pennsylvania, Maryland, West Virginia, and Virginia. It would be next to impossible to control this vast area or abate the nuisances thereon without practically depopulating it. It need not be considered further. A new supply must either be taken from a watershed capable of yielding an adequate quantity of water, or obtain it from artesian wells. There is no watershed near Washington which would furnish the water supply which is not open to the same objections as apply to the Potomac Basin. Even if it were possible to procure a new supply, the expense of purchase and that incident to policing would be far in excess of the expense connected with any proposition heretofore advanced for the purification of the present water supply. Artesian wells would not, owing to the geological formation of the District, be practicable. Filtration.—Filtration of water is accomplished in one of two ways, the rapid method of mechanical processes, or by the slow method of sand filtration. The mechanical method, while it removes the suspended matter from a water, performs the function of removing bacteria in a variable manner, depending on the character of the appliance, the method of operating, and the water to be filtered. The removal of the bacteria is what should be defined as filtration, and a filter which removes the bacteria successfully will remove the suspended matter: but filters may remove the suspended matters and fail to reduce the number of bacteria. This is usually what the mechanical filters do. Mechanical filtration would not be successful in removing the bacteria from the Potomac water on account of the large quantity of suspended matter. Household filtration has its advocates. The filtering apparatus best adapted for household purposes are those made of unglazed porcelain or infusorial earth, such as the Pasteur-Chamberland or the Berkfeld. These filters, if perfect (and very few of them are), will efficiently filter water for a short time only. They require a great deal of care and attention, and must be cleansed at frequent intervals, for if not, they become a greater menace than the raw water. They are also quite expensive and out of reach of the masses, those who require them most. You may enjoin and plead for people to boil their drinking water, but they will not do it unless threatened with a visitation of cholera, and then only at starts and intervals, it being proportional to the degree of their fright. My opinion is that if you desire people to use boiled water you must boil it for them. Sand filtration is the most practical solution; in fact, it seems to be the only way in which a large quantity of water can be purified and rendered potable. It was on account of the high death rate from typhoid fever that this system of water filtration was adopted and perfected by the European cities. Since its use the death rate from typhoid and other diseases has fallen to a very low rate. In view of the good results accomplished by their use of it, it is remarkable that no more than four of our American cities have adopted this system, and particularly Washington.

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