The source and quality of the water previously supplied has been sufficiently indicated in Appendix II. It was originally intended to filter the water, but the construction of filters was postponed from time to time until the fall of 1890, when the project was seriously taken up, and work was commenced in the spring of 1891. Three years were allowed for construction. In 1892, however, the epidemic of cholera came, killing 8605 residents and doing incalculable damage to the business interests of the city. The health authorities found that the principal cause of this epidemic was the polluted water-supply. To prevent a possible recurrence of cholera in 1893, the work of construction of the filters was pressed forward much more rapidly than had been intended. Electric lights were provided to allow the work to proceed nights as well as days, and as a result the plant was put in operation May 27, 1893, a full year before the intended time. Owing to the forced construction the cost was materially increased.
The new works take the raw water from a point one and a half miles farther up-stream, where it is believed the tide can never carry the city’s own sewage, as it did frequently to the old intake. The water is pumped from the river to settling-basins against heads varying with tide and the water-level in the basins from 8 to 22 feet. Each of the four settling-basins has an area of about 10 acres, and, with the water 6.56 feet deep, holds 20,500,000 gallons, or 82,000,000 gallons in all. The works are intended to supply a maximum of 48,000,000 gallons daily, but the present average consumption is only about 35,000,000 gallons (1892), or 59 gallons per head for 600,000 population. This consumption is regarded as excessive, and it is hoped that it will be reduced materially by the more general use of meters. The sedimentation-basins are surrounded by earthen embankments with slopes of 1:3, the inner sides being paved with brick above a clay layer. The water flows by gravity from these basins to the filters, a distance of 11⁄2 miles, through a conduit 81⁄2 feet in diameter. The flow of the water out of the basins and from the lower end of the conduit is regulated by automatic gates connected with floats, shown by Fig. 11, page 60.
The filters are 18 in number, and each has an effective area of 1.89, or 34 acres in all. They are planned to filter at a rate of 1.60 million gallons per acre daily, which with 16 filters in use gives a daily quantity of 48,000,000 gallons as the present limit of the works. The sides of the filters are embankments with 1:2 slopes. Both sides and bottoms have 20 inches of packed clay, above which are 4 inches of puddle, supporting a brick pavement laid in cement. The bricks are laid flat on the bottom, but edge-wise on the sides where they will come in contact with ice.
The main effluent-drain has a cross-section for the whole length of the filter of 4.73 square feet, or 1⁄17000 of the area of the filter; and even at the low rate of filtration proposed, the velocity in the drain will reach 0.97 foot. The drain has brick sides, 1.80 feet high, covered with granite slabs. The lateral drains are all of brick with numerous large openings for admission of water. They are not ventilated, and I am unable to learn that any bad results follow this omission.
The filling of the filters consists of 2 feet of gravel, the top being of course finer than the bottom layers, above which are 40 inches of sand, which are to be reduced to 24 inches by scraping before being refilled. The water over the sand, when the latter is of full depth, is 43 inches deep, and will be increased to 59 inches with the minimum sand-thickness. The apparatus for regulating the rate of filtration was described page 52. The cost of the entire plant, including 34 acres effective filter-surface, 40 acres of sedimentation-basins, over 2 miles of 81⁄2-foot conduit, pumping-machinery, sand-washing apparatus, laboratory, etc., was about 9,500,000 marks, or $2,280,000. This all reckoned on the effective filter area is $67,000 per acre, or $3.80 per head for a population of 600,000.
The death-rate since the introduction of filtered water has been lower than ever before in the history of the city, but as it is thought that other conditions may help to this result, no conclusions are as yet drawn.
| DEATHS IN HAMBURG FROM ALL CAUSES, AND FROM TYPHOID FEVER, BEFORE AND AFTER THE INTRODUCTION OF FILTERS. | |||
|---|---|---|---|
| Year. | Deaths from all Causes per 1000 Living. | Deaths from Typhoid Fever per 100,000 Living. | |
| 1880 | 24.9 | 26 | |
| 1881 | 24.1 | 30 | |
| 1882 | 23.7 | 27 | |
| 1883 | 25.2 | 25 | |
| 1884 | 25.1 | 26 | |
| 1885 | 25.3 | 42 | |
| 1886 | 29.0 | 71 | |
| 1887 | 26.6 | 88 | |
| 1888 | 24.5 | 54 | |
| 1889 | 23.5 | 43 | |
| 1890 | 22.0 | 27 | |
| 1891 | 23.4 | 24 | |
| 1892 | 41.1 | 34 | Cholera year. |
| 1893 | 20.2 | 18 | Filtered water from May 28. |
| 1894 | 17.9 | 7 | |
| 1895 | 19.0 | 11 | |
| 1896 | 17.3 | 6 | |
| 1897 | 17.0 | 7 | |
| 1898 | 17.5 | 5 | |
Average for 5 years, excluding cholera year, beforefiltration, 1887 to 1891 | 24.0 | 47.2 | |
Average for 5 years withfiltration, 1894 to 1898 | 17.7 | 7.2 | |
APPENDIX IX.
NOTES ON SOME OTHER EUROPEAN WATER-SUPPLIES.
Amsterdam.—The water is derived from open canals in the dunes. These canals have an aggregate length of about 15 miles, and drain about 6200 acres. The water, as it enters the canals from the fine dune-sand, contains iron, but this is oxidized and deposited in the canals. The water after collection is filtered. It has been suggested that by using covered drains instead of open canals for collecting the water, the filtration would be unnecessary; but, on the other hand, the cost of building and maintaining covered drains in the very fine sand would be much greater than that of the canals, and it is believed, also, that the water so collected would contain iron, the removal of which might prove as expensive as the present filtration. In 1887 filters were built to take water from the river Vecht, but the city has refused to allow the English company which owns the water-works to sell this water for domestic purposes, and it is only used for public and manufacturing purposes, only a fraction of the available supply being required. Leyden, the Hague, and some other Dutch cities have supplies like the dune supply of Amsterdam, and they are invariably filtered.
Antwerp is also supplied by an English company. The raw water is drawn from a small tidal river, which at times is polluted by the sewage of Brussels. It is treated by metallic iron in Anderson revolver purifiers, and is afterward filtered at a rather low average rate. The hygienic results are closely watched by the city authorities, and are said to be satisfactory.