--------------+-------+---------+-----------------+-------------------------- |Amount |Average | Average Rate | Bacterial Efficiency. | of |Thickness| of Filtration. | |Storage| of +--------+--------+--------+--------+-------- | Raw | Sand, |Imperial|Millions|Maximum.|Minimum.|Average. Company. |Water, | Feet. |Gallons | U. S. | | | | Days. | | per |Gallons | | | | | | Square |per Acre| | | | | |Foot per| Daily. | | | | | | Hour. | | | | --------------+-------+---------+--------+--------+--------+--------+-------- Chelsea | 12.0 | 4.0 | 1.75 | 2.19 | 99.92 | 99.62 | 99.86 West Middlesex| 5.6 | 2.75 | 1.25 | 1.56 | 99.94 | 91.48 | 99.79 Southwark & | | | | | | | Vauxhall | 4.1 | 2.5 | 1.5 | 1.88 | 100.00 | 84.33 | 97.77 Grand Junction| 3.3 | 2.25 | 1.63 | 2.05 | 99.98 | 84.03 | 99.31 Lambeth | 6.0 | 2.8 | 2.08 | 2.60 | 99.97 | 96.45 | 99.81 New River | 2.2 | 4.4 | 1.89 | 2.37 | 100.00 | 77.14 | 99.07 East London | 15.0 | 2.0 | 1.33 | 1.67 | 99.93 | 97.03 | 99.56 --------------+-------+---------+--------+--------+--------+--------+-------- APPENDIX VI. THE BERLIN WATER-WORKS. 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.