THE USE OF UNFILTERED SURFACE-WATERS.
The use of surface-water without filtration in Europe is comparatively limited. In Germany this use is now prohibited by the Imperial Board of Health. In Great Britain, Glasgow draws its supply unfiltered from Loch Katrine; and Manchester and some other towns use unfiltered waters from lakes or impounding reservoirs the watersheds of which are entirely free from population. The best English practice, however, as in Germany, requires the filtration of such waters even if they are not known to receive sewage, and the unpolluted supplies of Liverpool, Bradford, Dublin, and many other cities are filtered before use.
THE USE OF GROUND-WATER.[65]
Ground-waters are extensively used in Europe, and apparently in some localities the geological formations are unusually favorable to this kind of supply. Paris derives all the water it now uses for domestic purposes from springs, but has a supplementary supply from the river for other purposes. Vienna and Munich also obtain their entire supplies from springs, while Budapest, Cologne, Leipzig, Dresden, Frankfurt, many of the great French cities, Brussels, a part of London, and many other English cities derive their supplies from wells or filter-galleries, and among the smaller cities all over Europe ground-water supplies are more numerous than other kinds.
APPENDIX X.
LITERATURE OF FILTRATION.
The following is a list of a number of articles on filtration. The list is not complete, but it is believed that it contains the greater part of articles upon slow sand-filtration, and that it will prove serviceable to those who wish to study the subject more in detail.
Anklamm. Glasers Annalen, 1886, p. 48.
A description of the Tegel filters at Berlin, with excellent plans.
Baker. Engineering News.
Water purification in America: a series of descriptions of filters, as follows: Aug. 3, 1893, Lawrence filter and description of apparatus of screening sand and gravel; Apr. 26, 1894, filter at Nantucket, Mass.; June 7, 1894, filters at Ilion, N. Y., plans; June 14, 1894, filters at Hudson, N. Y.; July 12, 1894, filters at Zürich, Switzerland, plans; Aug. 23, 1894, filters at Mt. Vernon, N. Y., plans.
Bertschinger. Journal für Gas- und Wasserversorgung, 1889, p. 1126.
A record of experiments made at Zürich upon the effect of rate of filtration, scraping, and the influence of vaulting. Rate and vaulting were found to be without effect, but poorer results followed scraping. The numbers of bacteria in the lake-water were too low to allow conclusive results.
—— Journal für Gas- und Wasserversorgung, 1891, p. 684.
A farther account of the Zürich results, with full analyses and a criticism of Fränkel and Piefke’s experiments.
Bolton. Pamphlet, 1884.
Descriptions and statistics of London filters.
Böttcher and Ohnesorge. Zeitschrift für Bauwesen, 1876, p. 343.
A description of the Bremen works, with full plans.
Burton. Water-supply of Towns. London, 1894.
Pages 94-115 are upon filtration and mention a novel method of regulating the rate.
Codd. Engineering News, Apr. 26, 1894.
A description of a filter at Nantucket, Mass.
Cramer. Centralblatt für Bauwesen, 1886, p. 42.
A description of filters built at Brieg, Germany.
Crook. London Water-supply. London, 1883.
Delbruck. Allgemeine Bauzeitung, 1853, p. 103.
A general article on filtration; particularly valuable for notices of early attempts at filtration and of the use of alum.
Deutsche Verein von Gas- und Wasserfachmänner.
Stenographic reports of the proceedings of this society are printed regularly in the Journal für Gas- und Wasserversorgung, and the discussions of papers are often most interesting.
Drown. Journal Association Eng. Societies, 1890, p. 356.
Filtration of natural waters.
Fischer. Vierteljahresschrift für Gesundheitspflege, 1891, p. 82.
Discussion of papers on water-filtration.
Fränkel. Vierteljahresschrift für Gesundheitspflege, 1891, p. 38.
On filters for city water-works.
Fränkel and Piefke. Zeitschrift für Hygiene, 1891, p. 38, Leistungen der Sandfiltern.
E. Frankland. Report in regard to the London filters for 1893 in the Annual Summary of Births, Deaths, and Causes of Death in London and Other Great Towns, 1893. Published by authority of the Registrar-General.
P. Frankland. Proc. Royal Society, 1885, p. 379.
The removal of micro-organisms from water.
—— Proceedings Inst. Civil Engineers, 1886, lxxxv. p. 197.
Water-purification; its biological and chemical basis.
—— Trans. of Sanitary Institute of Great Britain, 1886.
Filtration of water for town supply.
Frühling. Handbuch der Ingenieurwissenschaften, vol. ii.
Chapter on water-filtration gives general account of filtration, with details of Königsberg filters built by the author and not elsewhere published.
Fuller. Report Mass. State Board of Health, 1892, p. 449.
Report Mass. State Board of Health, 1893, p. 453.
Accounts of the Lawrence experiments upon water-filtration for 1892 and 1893.
—— American Public Health Association, 1893, p. 152.
On the removal of pathogenic bacteria from water by sand filtration.
—— American Public Health Association, 1894, p. 64.
Sand filtration of water with special reference to results obtained at Lawrence, Mass.
Gill. Deutsche Bauzeitung, 1881, p. 567.
On American rapid filters. The author shows that they are not to be thought of for Berlin, as they would be more expensive as well as probably less efficient than the usual procedure.
—— Journal für Gas- und Wasserversorgung, 1892, p. 596.
A general account of the extension of the Berlin filters at Müggel. No drawings.
Grahn. Journal für Gas- und Wasserversorgung, 1877, p. 543.
On the filtration of river-waters.
—— Journal für Gas- und Wasserversorgung, 1890, p. 511.
Filters for city water-works.
—— Vierteljahresschrift für Gesundsheitpflege, 1891, p. 76.
Discussion of papers presented on filtration.
—— Journal für Gas- und Wasserversorgung, 1894, p. 185.
A history of the “Rules for Water-filtration” (Appendix I), with some discussion of them.
Grahn and Meyer. Reiseberichte über künstliche central Sandfiltration. Hamburg, 1876.
An account of the observations of the authors in numerous cities, especially in England.
Grenzmer. Centralblatt der Bauverwaltung, 1888, p. 148.
A description of new filters at Amsterdam, with plans.
Gruber. Centralblatt für Bakteriologie, 1893, p. 488.
Salient points in judging of the work of sand-filters.
Halbertsma. Journal für Gas- und Wasserversorgung, 1892, p. 43.
Filter-works in Holland. Gives sand, gravel, and water thickness, with diagrams.
—— Journal für Gas- und Wasserversorgung, 1892, p. 686.
Description of filters built by the author at Leeuwarden, Holland, with plans.
Hart. Proceedings Inst. of Civil Engineers, 1890, c. p. 217.
Description of filters at Shanghai.
Hausen. Journal für Gas- und Wasserversorgung, 1892, p. 332.
An account of experiments made for one year with three 16-inch filters at Helsingfors, Finland, with weekly analyses of effluents.
Hazen. Report of Mass. State Board of Health, 1891, p. 601.
Experiments upon the filtration of water.
—— Report of Mass. State Board of Health, 1892, p. 539.
Physical properties of sands and gravels with reference to their use in filtration. (Appendix III.)
Hunter. Engineering, 1892, vol. 53, p. 621.
Description of author’s sand-washing apparatus.
Kirkwood. Filtration of River-waters. New York, 1869.
A report upon European filters for the St. Louis Water Board in 1866. Contains a full account of thirteen filtration-works visited by the author, and of a number of filter-galleries, with a project for filters for St. Louis. This project was never executed, but the report is a wonderful work which appeared a generation before the American public was able to appreciate it. It was translated into German, and the German edition was widely circulated and known.
Koch. Zeitschrift für Hygiene, 1893.
Water-filtration and Cholera: a discussion of the Hamburg epidemic of 1892 in reference to the effect of filtration.
Kröhnke. Journal für Gas- und Wasserversorgung, 1893, p. 513.
An account of experiments made at Hamburg, as a result of which the author recommends the addition of cuprous chloride to the water before filtration to secure greater bacterial efficiency.
Kümmel. Journal für Gas- und Wasserversorgung, 1877, p. 452.
Operation of the Altona filters, with analyses.
—— Vierteljahresschrift für Gesundheitspflege, 1881, p. 92.
The water-works of the city of Altona.
—— Journal für Gas- und Wasserversorgung, 1887, p. 522.
An article opposing the use of rapid filters (David’s process).
—— Journal für Gas- und Wasserversorgung, 1890, p. 531.
A criticism of Fränkel and Piefke’s results, with some statistics of German and English filters. (The English results are taken without credit from Kirkwood.)
—— Vierteljahresschrift für Gesundheitspflege, 1891, p. 87.
Discussion of papers on filtration, with some statistics.
—— Vierteljahresschrift für Gesundheitspflege, 1892, p. 385.
The epidemic of typhoid-fever in Altona in 1891.
—— Journal für Gas- und Wasserversorgung, 1893, p. 161.
Results of experiments upon filtration made at Altona, and bacterial results of the Altona filters in connection with typhoid death-rates.
—— Trans. Am. Society of Civil Engineers, 1893, xxx. p. 330.
Questions of water-filtration.
Leslie. Trans. Inst. Civil Engineers, 1883, lxxiv. p. 110.
A short description of filters at Edinburgh.
Lindley. A report for the commissioners of the Paris Exposition of 1889 upon the purification of river-waters, and published in French or German in a number of journals, among them Journal für Gas- und Wasserversorgung, 1890, p. 501.
This is a most satisfactory discussion of the conditions which modern experience has shown to be essential to successful filtration.
Mason. Engineering News, Dec. 7, 1893.
Filters at Stuttgart, Germany, with plans.
Meyer and Samuelson. Deutsche Bauzeitung, 1881, p. 340.
Project for filters for Hamburg, with diagrams. Except in detail, this project is the same as that executed twelve years later.
Meyer. Deutsche Bauzeitung, 1892, p. 519.
Description of the proposed Hamburg filters, with diagrams.
—— The Water-works of Hamburg.
A paper presented to the International Health Congress at Rome, March 1894, and published as a monograph. It contains a full description of the filters as built, with drawings and views in greater detail than the preceding paper.
Mills. Special Report Mass. State Board of Health on the Purification of Sewage and Water, 1890, p. 601.
An account of the Lawrence experiments, 1888-1890.
—— Report Mass. State Board of Health, 1893, p. 543.
The Filter of the Water-supply of the City of Lawrence and its Results.
—— Trans. Am. Society of Civil Engineers, 1893, xxx. p. 350.
Purification of Sewage and Water by Filtration.
Neville. Engineering, 1878, xxvi. p. 324.
A description of the Dublin filters, with plans.
Nichols. Report Mass. State Board of Health, 1878, p. 137.
The filtration of potable water.
Oester. Gesundheits-Ingenieur, 1893, p. 505.
What is the Rate of Filtration? A purely theoretical discussion.
Orange. Trans. Inst. Civil Engineers, 1890, c. p. 268.
Filters at Hong Kong.
Pfeffer. Deutsche Bauzeitung, 1880, p. 399.
A description of filters at Liegnitz, Germany.
Piefke. Results of Natural and Artificial Filtration. Berlin, 1881.
Pamphlet.
—— Journal für Gas- und Wasserversorgung, 1887, p. 595. Die Principien der Reinwassergewinnung vermittelst Filtration.
A sketch of the theory and practical application of filtration.
—— Zeitschrift für Hygiene, 1889, p. 128. Aphorismen über Wasserversorgung.
A discussion of the theory of filtration, with a number of experiments on the thickness of sand-layers, etc.
Piefke. Vierteljahresschrift für Gesundheitspflege, 1891, p. 59.
On filters for city water-works.
Fränkel and Piefke. Zeitschrift für Hygiene, 1891, p. 38.
Leistungen der Sandfiltern. An account of the partial obstruction of the Stralau filters by ice, and a typhoid epidemic which followed. Experiments were then made upon the passage of cholera and typhoid germs through small filters.
Piefke. Journal für Gas- und Wasserversorgung, 1891, p. 208. Neue Ermittelungen über Sandfiltration.
The above mentioned experiments being objected to on certain grounds, they were repeated by Piefke alone, confirming the previous observations on the passage of bacteria through filters, but under other conditions.
—— Zeitschrift für Hygiene, 1894, p. 151, Über Betriebsführung von Sandfiltern.
A full account of the operation of the Stralau filters in 1893, with discussion of the efficiency of filtration, etc.
Plagge and Proskauer. Zeitschrift für Hygiene, 11. p. 403.
Examination of water before and after filtration at Berlin, with theory of filtration.
Reincke. Bericht über die Medicinische Statistik des Hamburgischen Staates für 1892.
Contains a most valuable discussion of the relations of filtration to cholera, typhoid fever, and diarrhœa, with numerous tables and charts. (Abstract in Appendix II.)
Reinsch. Centralblatt für Bakteriologie, 1895, p. 881.
An account of the operation of the Altona filters. High numbers of bacteria in the effluents have often resulted from the discharge of sludge from the sedimentation-basins onto the filters, due to the interference of ice on the action of the floating outlet for the basins, and this, rather than the direct effect of cold, is believed to be the direct cause of the low winter efficiency. The author urges the necessity of a deeper sand-layers in no case less than 18 inches thick.
Renk. Gesundheits-Ingenieur, 1886, p. 54.
—— Über die Ziele der künstliche Wasserfiltration.
Ruhlmann. Wochenblatt für Baukunde, 1887, p. 409.
A description of filters at Zürich.
Salbach. Glaser’s Annalen, 1882.
Filters at Groningen, Holland, built in 1880. Alum used.
Samuelson. Translation of Kirkwood’s “Filtration of River-waters” into German, with additional notes especially on the theory of filtration and the sand to be employed. Hamburg, 1876.
Samuelson. Filtration and constant water-supply. Pamphlet. Hamburg, 1882.
—— Journal f. Gas- und Wasserversorgung, 1892, p. 660.
A discussion of the best materials and arrangement for sand-filters.
Schmetzen. Deutsche Bauzeitung, 1878, p. 314.
Notice and extended criticism of Samuelson’s translation of Kirkwood.
Sedden. Jour. Asso. Eng. Soc., 1889, p. 477.
In regard to the sedimentation of river-waters.
Sedgwick. New England Water-works Association, 1892, p. 103.
European methods of Filtration with Reference to American Needs.
Sokal. Wochenschrift der östreichen Ingenieur-Verein, 1890, p. 386.
A short description of the filters at St. Petersburg, and a comparison with those at Warsaw.
Sturmhöfel. Zeitschrift f. Bauwesen, 1880, p. 34.
A description of the Magdeburg filters, with plans.
Tomlinson. American Water-works Association, 1888.
A paper on filters at Bombay and elsewhere.
Turner. Proc. Inst. Civil Engineers, 1890, c. p. 285.
Filters at Yokohama.
Van der Tak. Tijdschrift van de Maatschapping van Bouwkunde, 1875(?).
A description (in Dutch) of the Rotterdam water-works, including the wooden drains which caused the trouble with crenothrix, and which have since been removed. Diagrams.
Van Ijsselsteyn. Tijdschrift van het Koninklijk Instituut van Ingenieurs, 1892-5, p. 173.
A description of the new Rotterdam filters, with full drawings.
Veitmeyer. Verhandlungen d. polyt. Gesell. zu Berlin, April, 1880.
Filtration and purification of water.
Wolffhügel. Arbeiten aus dem Kaiserliche Gesundheitsamt, 1886, p. 1.
Examinations of Berlin water for 1884-5, with remarks showing superior bacterial efficiency with open filters.
—— Journal für Gas- u. Wasserversorgung, 1890, p. 516.
On the bacterial efficiency of the Berlin filters, with diagrams.
Zobel. Zeitschrift des Vereins deutsche Ingenieure, 1884, p. 537.
Description of filters at Stuttgart.
OTHER LITERATURE.
Many scientific and engineering journals publish from time to time short articles or notices on filtration which are not included in the above list. Among such journals none gives more attention to filtration than the Journal für Gasbeleuchtung und Wasserversorgung, which publishes regularly reports upon the operation of many German filters, and gives short notices of new construction. The first articles upon filtration in this journal were a series of descriptions of German water-works in 1870-73, including descriptions of filters at Altona, Brunswick, Lübeck, etc. Stenographic reports of many scientific meetings have been published, particularly since 1890, and since 1892 there has been much discussion in regard to the “Rules for Filtration” given in Appendix I.
A Report of a Royal Commission to inquire into the water-supply of the metropolis, with minutes of evidence, appendices, and maps (London, 1893-4), contains much valuable material in regard to filtration.
The monthly reports of the water examiner, and other papers published by the Local Government Board, London, are often of interest.
The German “Verein von Gas- u. Wasserfachmänner” prints without publishing a most useful annual summary of German water-works statistics for distribution to members. Many of the statistics given in this volume are from this source.
Description of the filters at Worms was given in the Deutsche Bauzeitung, 1892, p. 508; of the filters at Liverpool in Engineering, 1889, p. 152, and 1892, p. 739. The latter journal also has given a number of descriptions of filters built in various parts of the world by English engineers, but, excepting the articles mentioned in the above list, the descriptions are not given in detail.
MORE RECENT ARTICLES.
The following are a few of the more important articles which have appeared since the first edition of this book. In addition many articles of current interest have appeared in the technical journals, particularly in the journals mentioned above.
Clark. Reports of Mass. State Board of Health, 1894 to 1897, inclusive.
Articles on the filtration of water, giving accounts of experiments at the Lawrence Experiment Station, and records of the operation of the Lawrence city filter. These experiments are directed principally to the removal of bacteria from sewage-polluted waters.
—— Jour. New England Water Works Assoc., XI., p. 277.
Removal of Iron from Ground Waters. A description of certain experiments.
Fowler. Jour. New England Water Works Assoc., XII., p. 209.
The Operation of a Slow Sand Filter. A most helpful and thorough description of the operation of sand filters at Poughkeepsie for a long period of years.
Fuller. Water Purification at Louisville. D. Van Nostrand Co., 1898.
A report upon a series of most exhaustive experiments carried out at Louisville, directed principally to the clarification of excessively muddy waters. Contains a full account of methods of coagulation, and of experiments with the electrical treatment of water.
—— Report on Water Filtration at Cincinnati. City document, 1899.
Account of experiments with sand filters, with and without coagulants, and with other processes applied to the Ohio River water at Cincinnati.
Gill. Filters at Muggel. Proc. Institute of Civil Engineers, 1894-5; vol. 119, p. 236.
A description of the new vaulted filter plant designed by the author for Berlin, Germany. Plans and views.
Goetze. Journal für Gasbeleuchtung und Wasserversorgung, 1897, p. 169.
Selbstthätige Wasseraustrittsregler besonders für Filter. A description of the automatic regulating device for filters used at Bremen.
—— Zeitschrift des Vereines deutscher Ingenieure, XXX.
Reinigung des Trinkwassers in Bremen durch mehrmalige Sandfiltration. A description of the method of double filtration used at Bremen, giving results obtained in full. No drawings.
Grahn. Journal für Gasbeleuchtung und Wasserversorgung, 1895.
Water purification plant at the city of Magdeburg. A description of the old plant, and the changes which have been made in it to increase its capacity, and make it conform to the requirements of the German official instructions regarding filtration. Many illustrations and plans.
Halbertsma. Journal für Gasbeleuchtung und Wasserversorgung, 1896.
Die Resultate der doppelten Filtration zu Schiedam. A description of double filtration at Schiedam, with the bacterial results for the two years, 1894 and 1895, showing an average bacterial efficiency of 99.76 per cent.
Hazen. Report to Filtration Commission, Pittsburgh. City document, 1899.
A description of experiments upon the treatment of the Allegheny River water by sand and mechanical filters.
—— Ohio State Board of Health Report, 1897, p. 154.
Report on the Mechanical Filtration of the Public Water Supply of Lorain. Gives the results of a five-weeks test of the Jewell mechanical filters at Lorain, treating Lake Erie water.
Kemna. The Biology of Sand Filtration. Read before the annual convention of the British Association of Water Works Engineers. Abstract in Engineering News, XLI., p. 419.
Describing organisms which develop in open sand filters, both animal and vegetable, and their effects upon the process. A quite full account of the author’s extended experience, and the only paper treating this subject.
Magar. Journal für Gasbeleuchtung und Wasserversorgung, 1897, p. 4.
Reinigungsbetrieb der offener Sandfilter des Hamburger Filterwerkes in Frostzeiten. A new method of cleaning open filters in winter without the removal of the ice.
Panwitz. Arbeiten aus dem Kaiserlichen Gesundheitsamte, XIV., p. 153.
Die Filtration von Oberflächenwasser in den deutschen Wasserwerken während der Jahre 1894 bis 1896.
A description of the filtration works in Germany, and the results obtained from them, particularly from the point of view of bacterial efficiency. Results are graphically shown by a series of charts.
Reynard. Le Génie Civil, 1896, XXVIII., p. 321.
Purification of water with the aid of metallic iron. Describing the works of the Compagnie Général des Eaux for supplying the suburbs of Paris with filtered water, the capacity of the works being over 23,000,000 gallons daily.
Weston. Rhode Island State Board of Health, 1894.
Report of the Results Obtained with Experimental Filters at the Pattaconset Pumping Station of the Providence Water Works. Relates particularly to the bacterial purification obtained with rapid filtration aided by sulphate of alumina. These were the first systematic experiments made with mechanical filters.
Wheeler. Journal of the New England Water Works Assoc., XI., p. 301. Covered Sand Filter at Ashland, Wis.
A description of the covered filters built by the author at Ashland Wis. for the purification of the bay water. Views and drawings.
APPENDIX XI.
THE ALBANY WATER-FILTRATION PLANT.
(Abridged from Proceedings American Society of Civil Engineers, Nov. 1899.)
Albany, N. Y., was originally supplied with water by gravity from certain reservoirs on small streams west and north of the city. In time, with increasing consumption, the supply obtained from these sources became inadequate, and an additional supply from the Hudson River was introduced. The water was obtained from the river through a tunnel under the Erie Basin, and a pumping-station was erected in Quackenbush Street to pump it to reservoirs, one of which served also as the distributing point for one of the gravity supplies. The intake, which was used first in 1873, drew water from the river opposite the heart of the city. In recent years, the amount of water drawn from this source has greatly exceeded that obtained from the gravity sources.
The Hudson River, at the point of intake, has a drainage area of 8240 square miles. Of this, 4541 square miles are tributary to the Hudson above Troy, 3493 are tributary to the Mohawk, and 168 are tributary to the Hudson below the Mohawk.
The minimum flow may be estimated at 1657 cubic feet per second, or 1,060,000,000 gallons per 24 hours, or at least fifty times the maximum consumption.
The cities and larger towns upon the river above the intake, with estimated populations and distances, are as follows:
| MOST IMPORTANT CITIES, TOWNS, AND VILLAGES ON THE WATERSHED OF THEHUDSON ABOVE ALBANY. | |||||
|---|---|---|---|---|---|
| Place. | County. | Approximate Distance above Intake, Miles. | Population in | ||
| 1880. | 1890. | 1900. (Estimated.) | |||
| Troy | Rensselaer | 4 | 56,747 | 60,956 | 65,470 |
| Watervliet | Albany | 4 | 8,820 | 12,967 | 19,040 |
| Green Island | Rensselaer | 5 | 4,160 | 4,463 | 4,788 |
| Cohoes | Albany | 8 | 19,416 | 22,509 | 26,450 |
| Lansingburg | Rensselaer | 8 | 7,432 | 10,550 | 14,980 |
| Waterford | Saratoga | 9 | (1,822) | 1,822 | (1,822) |
| Schenectady | Schenectady | 28 | 13,655 | 19,002 | 26,450 |
| Hoosic Falls | Rensselaer | 44 | 4,530 | 7,014 | 10,860 |
| Amsterdam | Montgomery | 44 | 9,466 | 17,336 | 31,730 |
| Glens Falls | Warren | 49 | 4,900 | 9,509 | 18,450 |
| Saratoga Springs | Saratoga | 51 | 8,421 | 11,975 | 17,010 |
| Johnstown | Fulton | 56 | 5,013 | 7,768 | 12,040 |
| Gloversville | Fulton | 58 | 7,133 | 13,864 | 26,930 |
| North Adams, Mass. | Berkshire | 68 | 10,191 | 16,074 | 25,340 |
| Adams, Mass. | Berkshire | 75 | 5,591 | 9,213 | 15,181 |
| Little Falls | Herkimer | 82 | 6,910 | 8,783 | 11,160 |
| Utica | Oneida | 107 | 33,914 | 44,007 | 57,090 |
| Rome | Oneida | 127 | 12,194 | 14,991 | 18,430 |
| 32 villages | 52,523 | 61,869 | 76,194 | ||
| Total, not including rural population | 272,838 | 354,672 | 479,415 | ||
| Per square mile | 33 | 43 | 59 | ||
Without entering into a detailed discussion, it may be said that the amount of sewage, with reference to the size of the river and the volume of flow, is a fraction less than that at Lawrence, Mass., where a filter-plant has also been constructed, but the pollution is much greater than that of most American rivers from which municipal water-supplies are taken.
The filtration-plant completed in 1899 takes the water from a point about two miles above the old intake. Pumps lift the water to the sedimentation-basin, from which it flows to the filters and thence through a conduit to the pumping-station previously used.