Dollar Weekly Mirror

Water Supply of London.—The double problem, says the Boston Telegraph, of supplying a populous city with pure water and draining off the impure, is one of the most important and difficult which science and art have to deal with. Its importance and difficulties both increase with the increase of population, and in a geometrical ratio. Without adequate drainage, the better the supply of water the worse for the public health.—But ample drainage, when it is made into the rivers, damages the purity of the water supply. This has been the case with the vast British metropolis. Before it had anything more than superficial drainage, it commenced distributing water from the Thames, by aqueduct. The plenty of water made the deficiency of drainage pestilential and intolerable. Then was commenced and rapidly carried out, a vast subterranean system of sewers, which carried the waste water, and with it an immense amount of insoluble filth into the Thames. Very soon a portion of this filth was found coming back again with the water supply. So general was the conviction that this impurity of the water caused or aggravated the cholera, that the water companies deriving their supply from the Thames were obliged to go above the mouths of the principal sewers with their suction.

But the convenience and value of thorough drainage soon extended that system from London to the suburban towns and villages, and thus not only the Thames but all the smaller accessible streams became dreadfully impure. An examination of the water, 44,000,000 gallons of which was supplied to the metropolis by nine companies in 1851, rather frightened the delicate by its results. It appeared that along with the pure element about 80 tons of "solid constituents" were distributed to the people daily, of which, in the decent language of the chemist, about 12 tons consisted of "organic matter!" Philosophers and engineers were consulted, and the water companies were obliged, by an act of Parliament, in 1852, to resort to various expedients for purifying and preserving pure their supply of water, the chief of which were covered reservoirs and immense filtering beds. The entire supply of each of the companies, except one, which only supplies 3000 houses, flows through a carefully prepared filtering bed of coarse sand before any of it is distributed. The largest of these beds is 12 acres in extent, and in the aggregate they measure over 40 acres.

During the past year a scientific analysis of the water of the various companies has been made to test the value of the above arrangement. The results of it are contained in a recent "blue book." It appears that the "organic matter" distributed daily in a given quantity of water has been reduced three fourths, though the "solid constituents" in general are not sensibly diminished. The water is not softer, but a trifle harder than in 1851. Thus the filtering beds, the total supply of water being about double what it was in 1851, detain about 18 tons of "organic matter" daily. But the other matters thrown into the rivers by drainage, and some of which render the water hard, being in solution, pass on without being arrested, not being arrestible by any mechanical means.

This shows the vast importance of a drainage which shall not empty into the rivers. If such a drainage could be effected, the sediment obtained would be of incalculable value for agricultural purposes. Taking into view together the value of pure water and manure in the neighborhood of great cities, it is certainly time that a great effort should be made to divert the sewers from the rivers, and we may also say the harbors. The following extract gives the present extent of the London Water Works.

The supply of water to the metropolis has now reached the enormous quantity of upwards of 81 millions of gallons per day, it having been nearly doubled in the short space of six years. It is now furnished to 328,561 of the 340,000 houses which now form the aggregate within the Registrar General's district. Thus, the average daily supply of water for all purposes, which in 1850 was 164 gallons per house, is now, in 1856, 246 gallons per house. The total nominal engine power employed, and in reserve, is equal to 7320 horses. The mains and branch pipes for bringing the water from the several sources and distributing it in the districts, exclusive of the private service pipes, form a total length of 2086 miles. The filter beds cover an area of upwards of forty acres. Before the passing of the Metropolis Water Act of 1852, considerably more than half the supply was not filtered; subsiding reservoirs were in such case the only means of clearing the water of impurities in suspension; these are now for the most part, employed as well as the filter beds, the total area of subsiding reservoirs in use being upwards of 141 acres in extent.—The filtered water is stored in fourteen covered reservoirs, comprising an area of nearly fifteen acres, and in four uncovered reservoirs, of not quite three acres, which are beyond 5 miles distant from St. Paul's. The cost of the new works, executed under the Metropolis Water Act, 1852, and the recent acts of the several companies, has amounted to £2,282,824, making, with the former expenditure, as shown by the returns of 1850, the cost of the entire water works of the metropolis upwards of seven millions sterling. Even this amount, however, will fall short of the total expenditure for the intermediate outlay between the former returns and the passing of the new Acts, and the cost of many works in hand, but not yet completed, are not included in this sum.