THE CITY WATER SUPPLY. ADOLPH GEHRMANN, M. D., CITY BACTERIOLOGIST. DURING the two years, 1895 and 1896, an extended examination of the city water supply by chemic and bacteriologic methods was systematically undertaken. In the early part of 1895 analyses were made weekly from the various tunnels extending from the cribs in Lake Michigan, but later a systematic daily analysis of samples from each of these sources of supply was established. This series has regularly included analyses from five sources daily, except Sundays and holidays, when the laboratory was closed. In the accompanying table four of these analyses are presented for each day. The other analysis, that of the tap-water in the laboratory, is not included and has not been taken into account in making the tabulations of the sanitary quality of the water supply, because it was mixed water and contained, in a large proportion, the water of Chicago-avenue pumping station, which would cause a misconception of the real state of affairs, as it would be using the data from one source of supply twice. The methods used in making these analyses are the same as those that were described in the annual report of the DEPARTMENT for 1894. The bacteriologic methods are those ordinarily employed in water analyses for the determination of pathogenic bacteria. In the column of presence of pathogenic bacteria in the table, the percentages given do not indicate the typhoid bacillus, but do indicate any bacteria that were isolated which, by injection experiments, were found capable of causing the death of animals. Among the cultures of bacteria isolated the Bacillus coli communis has been very frequently found. While cultures giving all of the characters which are assigned to the typhoid bacillus were not found, still, several bacteria were isolated at different times which gave cultural and experimental results so closely resembling the typhoid bacillus that it is quite possible we were dealing with that specific organism. Other bacteria, as various forms of Proteus, are also included among the pathogenic bacteria. In fact, whenever an organism was found which was capable of causing the death of a guinea pig by an injection experiment that fact is included in the characterization. In the tables presented we have, first, the daily analyses of the samples derived from the four tunnels collected at the pumping stations on the shore, arranged in months; then the average analyses of the daily samples for each month, the average analyses being given separately for each pumping station; and finally, the average analyses from each of the pumping stations from all the analyses made during the year, and an average of these final four analyses which may be accepted as a very fair statement of the sanitary quality of the water during the entire year. Similar tables for 1895 are not introduced because of their size and because they have no special interest other than those that are shown in the 1896 tables. From the yearly average it is readily seen that the Fourteenth-street water, or that obtained from a point four miles in the lake, is decidedly better than any of the others. The other three stations, which are from points two miles in the lake, are of about the same sanitary quality; Chicago avenue and Lake View being the worst, while Hyde Park is somewhat better. The average of all of the chemic and bacteriologic analyses of water would cause the characterization of the public water supply of Chicago during the year 1896 to be "suspicious. On twenty-three days, or nearly ten per cent. of the days examined, the water contained bacteria of a pathogenic character and the colony count shows a daily average of over six thousand bacteria to the cubic centimeter, which is far above the limit for potable water. Although the supply from the four-mile crib through the Fourteenth-street tunnel shows the best average analysis, the best that can be said of it is that the degree of contamination is less than that of the intakes nearer shore.* * A tabulation of the sanitary characterizations of the water supplied by the four different tunnels for the period from January 1, 1896, to about the middle of August, was made by the ASSISTANT COMMISSIONER for the information of the Mayor and a special committee on the water supply. Contrary to a general preconception, the Fourteenthstreet tunnel water did not show the best in this tabulation-the order being as follows: Hyde Park, 81 per cent. "good" or "usable," 19 per cent. "suspicious" or "bad;" Chicago avenue, 80 per cent. "good" or "usable," 20 per cent. "suspicious" or "bad;" Fourteenth street, 79 per cent. "good" or "usable," 21 per cent. "suspicious" or "bad;" Lake View, 55 per cent. "good" or "usable," 45 per cent. "suspicious" or "bad." From time to time sudden and unaccountable contamination had been noted in all the sources of supply, but chiefly that from the four-mile crib. The result of this tabulation led to further search, the details of which are given in the following report of Dr. GEHRMANN, dated September 8, 1896: "The dumping of dredgings from scows in the lake has been done to such an extent that your attention should be directed to this form of contamination of the water supply. The scows are towed out midway between the Van Buren-street opening of the Government pier and the four-mile crib and there emptied. We have seen and recorded the dumping of tows as follows: September 2, 12 m., tug Mentor, F. & C. Co., two scows. September 2, 12 m., tug William Rollar, W. A. McGiles, D. Co., one scow. September 2, 2.30 p. m., tug Commodore, C. D. & D. Co., two scows. September 3, 8.30 a. m., tug W. Rollar, one scow. September 3, 2 p. m., tug W. Rollar, two scows. September 3, 4 p. m., tug Mentor, one scow. September 4, 8 a. m., tug William Rollar, one scow. September 4, 2 p. m., tug William Rollar, two scows. "Samples of water for analysis were collected at points outside the area where the dumping is being done, and over this area at various times, from immediately after the dredgings were discharged until two hours afterwards. The result of putting dredgings into the lake is easily seen by the discoloration of the water. Areas of dirty water may be traced for a mile in different directions, according to the direction of the wind. Examination of water in these discolored areas, when compared with examinations outside of the areas and with the examination of samples that were collected last year at different points between the Hyde Park crib, the four-mile crib and the outer Lake View crib, show that the contamination is serious. The suspended matter in the samples shows epithelial scales, portions of hair and vegetable cells in great variety. The bacteriologic cultures of the water show that intestinal and decomposition bacteria are always present. Varieties found include Bacillus coli communis and Proteus vulgaris. The dumping of dredgings into the lake extends the area of contamination that already exists from the river and those sewers that empty along the water front. The dredgings are placed so far from shore that they can easily reach the cribs. The sudden and apparently unaccountable changes in the character of the water from the intakes are in part due to the presence of these dredgings. Some regulation should be made in regard to this matter so that the constant possibility of endangering the purity of the water supply can be avoided." Action was at once taken in accordance with Dr. GEHRMANN'S recommendation, and all dumping in localities likely to affect the intakes was absolutely prohibited. Thereafter the quality of the Fourteenth-street supply improved to such an extent as to make the average for the year the best of the four sources.-F. W. R. There is an area of continually contaminated water along the lake front. This area under favorable conditions-that is, easterly or northeasterly winds and no rainfall-extends only a short distance from shore, but when rainfall occurs and westerly winds prevail the area gradually extends further and further into the lake. During the greater part of the year this area of contaminated water extends between a mile and a half and two miles from shore, but occasionally it may extend a much greater distance, as will be seen in the table of analyses of samples taken as far as twelve miles out into the lake. To attempt to obtain pure water by locating cribs beyond this line of permanent contamination leads to a false security, because at one time the area of contamination may be determined as extending a certain distance into the lake, at another time it may have receded, or again, it may have extended to a much greater distance. From the daily analyses warnings have been issued to the public as to the quality of the supply. The samples are brought to the laboratory at 9 o'clock in the morning and the ammonia determinations, oxygen consumed, and chlorides are determined at once, the report being on the COMMISSIONER'S desk at 11 o'clock. The bacteriologic work is begun at once, but, of course, is not finished the same day. Within the next three days a report is rendered which is taken into account in the preparation of the final opinion as to the quality. The chemic analyses always give sufficient evidence to prepare the warning statements to the public, the results as found simply indicating the conditions which would accompany the contamination, and which would possibly give rise to an epidemic of typhoid fever or intestinal disease. In looking over the tables it will be found that the bacteriologic results, giving evidence of contamination, occur one or two days after the first evidence of the altered quality of the water, as already determined by the chemic analyses. We have, therefore, come to use the results of the chemic examination at once and not wait for the final bacteriologic findings before making a statement to the public. From the daily analyses a statement of the weekly sanitary quality of the water is prepared. This has been arranged in the form of a curve, so that one may see graphically the changes in the quality of the water at different times during the year. The methods of determining this statement of the sanitary quality is as follows: Four qualities are designated: "good," "usable," "suspicious" and "bad;" and three degrees of each. When the supply is designated as "good" or "usable," the samples have shown an entire absence of any quality capable of producing disease. When designated as "suspicious" or "bad," the samples have shown qualities, at one or more times during the week, capable of producing disease. The quality of "good" is determined by an entire absence of nitrates and nitrites; by traces only of free ammonia; by not more than .001 part per 100 000 of albuminoid ammonia; by entire absence of pathogenic bacteria; and by a count of bacteria of less than 500 per cc. The quality of "usable" is determined by an entire absence of nitrates or nitrites; by free ammonia not in excess of .004 part per 100 000 at any time; by albuminoid ammonia not in excess of .009 part per 100 000 at any time; by an entire absence of pathogenic bacteria; and by a count of bacteria not more than 1000 to the cc. The quality of "suspicious" is determined by any presence of nitrates or nitrites; by any excess of free and albuminoid ammonia beyond .004 and .009 respectively; and by any excess beyond 1000 bacteria to the cubic centimeter, whether it occurs on one or more days. |