The original works were built by an English company in 1856, and were sold to the city in 1873 for $7,200,000.

The water was taken from the river Spree at the Stralau Gate, which was then above, but is now surrounded by, the growing city. The water was always filtered, and the original filters remained in use until 1893, when they were supplanted by the new works at Lake Müggel. Soon after acquiring the works the city introduced water from wells by Lake Tegel as a supplementary supply, but much trouble was experienced from crenothrix, an organism growing in ground-waters containing iron, and in 1883 this supply was replaced by filtered water from Lake Tegel. With rapidly-increasing pollution of the Spree at Stralau the purity of this source was questioned, and in 1893 it was abandoned (although still held as a reserve in case of urgent necessity), the supply now being taken from the river ten miles higher up, at Müggel.

The watershed of the Spree above Stralau, as I found by map measurement, is about 3800 square miles; the average rainfall is about 25 inches yearly. At extreme low water the river discharges 457 cubic feet per second, or 295 million gallons daily, and when in flood 5700 cubic feet per second may be discharged. The city is allowed by law to take 46 million gallons daily for water-supply, and this quantity can be drawn either at Stralau or at Müggel.

Above Stralau the river is polluted by numerous manufactories and washing establishments, and by the effluent from a considerable part of the city’s extensive sewage farms. The shipping on this part of the river also is heavy, and sewage from the boats is discharged directly into the river. The average number of bacteria in the Spree at this point is something over ten thousand per cubic centimeter, and 99.6 per cent of them were removed by the filters in 1893.

The watershed of the Spree above the new water-works at Müggel I found by map measurement to be 2800 square miles, and the low water-discharge is said to be 269 million gallons daily. The river at this point flows through Lake Müggel, which forms a natural sedimentation-basin, and the raw water is quite clear except in windy weather.

There were 16 towns on the watershed with populations above 2000 each in 1890, and an aggregate population of 132,000, which does not include the population of the smaller places or country districts. None of these places purify their sewage so far as they have any. Fürstenwalde with a population of 12,935, and 22 miles above Müggel, has surface sewers discharging directly into the river. Above Fürstenwalde the river runs through numerous lakes which probably remove the effect of the pollution from the more distant cities. There is considerable shipping on the river for some miles above Fürstenwalde (which forms a section of the Friedrich Wilhelm Canal), but hardly any between Müggel and Fürstenwalde. The raw water at Müggel contains two or three hundred bacteria per cubic centimeter, and is thus a comparatively pure water before filtration. It is slightly peaty and the filtered water has a light straw color.

Lake Tegel, which supplies the other part of the city’s supply, is an enlargement of the river Havel. The watershed above Tegel I find to be about 1350 square miles, and the annual rainfall is about 22 inches. The low water-discharge is said to be 182 million gallons daily, and the city is allowed by law to take 23 million gallons for water-supply.

There were ten towns upon the watershed with populations above 2000 each in 1890, and with an aggregate population of 44,000. Of these Tegel is directly upon the lake with a population of 3000, and Oranienburg, 14 miles above, has a population of 6000 and is rapidly increasing. The shipping on the lake and river is heavy. The lake water ordinarily contains two or three hundred bacteria per cubic centimeter. The lake is shallow and becomes turbid in windy weather.

There are 21 filter-beds at Tegel with a combined area of 12.40 acres to furnish a maximum of 23 million gallons of water daily, and 22 filters at Müggel with a combined area of 12.7 acres to deliver the same quantity. Twenty-two more filters will be built at Müggel within a few years to purify the full quantity which can be taken from the river. All of these filters are covered with brick arches supported by pillars about 16 feet apart from centre to centre in each direction, and the whole is covered by nearly 3 feet of earth, making them quite frost-proof. The original filters at Stralau were open, but much difficulty was experienced with them in winter.

The bottom of the filters at Tegel consists of 8 inches of concrete above 20 inches of packed clay and with 2 inches of cement above, and slopes slightly from each side to the centre. The central drain goes the whole length of the filters and has a uniform cross-section of about ¹⁄₇₃₀₀ of the area of the whole bed. There are no lateral drains, but the water is brought to the central drain by a twelve-inch layer of stones as large as a man’s fist; above this there is another foot of gravel of graded sizes supporting two feet of fine sand, which is reduced by scraping to half its thickness before the sand is replaced. The average depth of water above the sand is nearly 5 feet. The filters are not allowed to filter at a rate above 2.57 million gallons per acre daily, and at this rate with 70 per cent of the area in service the whole legal quantity of water can be filtered. The filters work at precisely the same rate day and night, and the filtered water is continuously pumped as filtered to ample storage reservoirs at Charlottenburg. The pumps which lift the water from the lake to the filters work against a head of 14 feet. The apparatus for regulating the rate of filtration was described on page 51.

As yet no full description of the Müggel works has been published, but they resemble closely the Tegel works. Both were designed by or under the direction of the late director of the water-works, Mr. Henry Gill.

The average daily quantity of water supplied for the fiscal year ending March 31, 1893, was 29,000,000 gallons daily, which estimate allows 10 percent for the slip of the pumps. Of this quantity 9,650,000 was furnished by Stralau and 19,350,000 by Tegel. The greatest consumption in a single day was 43,300,000 gallons, or 26.6 gallons per head, while the average quantity for the year was 18.4 gallons per head. All water without exception is sold by meter, the prices ranging from 27.2 cents a thousand gallons for small consumers to 13.6 cents for large consumers and manufacturers. The average receipts for all water pumped, including that used for public purposes and not paid for, were 15.4 cents a thousand gallons, against the cost of production, 9.8 cents, which covers operating expenses, interest on capital, and provision for sinking fund. This leaves a handsome net profit to the city. On account of the comparatively high price of the city water and the ease with which well-water is obtained, the latter is almost exclusively used for running engines, manufacturing purposes, etc., and this in part explains the very low per-capita consumption.

The volume of sewage, however, for the same year, including rain-water, except during heavy showers, was only 29 gallons per head, showing even with the private water-supplies an extraordinarily low consumption.

The friction of the water in the 4.75 miles of 3-foot pipe between Tegel and the reservoir at Charlottenburg presents an interesting point. When well-water with crenothrix was pumped, the friction rose to 34.5 feet, when the velocity was 2.46 feet per second. According to Herr Anklamm, who had charge of the works at the time, the friction was reduced to 19.7 feet when filtered water was used and after the pipe had been flushed, and this has not increased with continued use. He calculated the friction for the velocity according to Darcy 15.0 feet, Lampe 17.8 feet, Weisbach 18.7 feet, and Prony 21.5 feet.