THE WATER QUESTION AT PHILADELPHIA.
MAYOR ASHBRIDGE, of Philadelphia, it will be remembered, appointed a commission of experts to investigate the problem of that city’s water supply, with a view to its extension and improvement. The commissioners have issued a preliminary report, from which we gather that they have the work well in hand. They state that they have visited the watersheds available for supply in the Schuylkill, the Perkiomen, the Lehigh and Upper Delaware valleys, as well as various points along the courses of the Schuylkill and Delaware. They have also observed the nature of the country, its cultivation, its population, and the sources of pollution to which its waters are subject. They report that they are prepared to give proper consideration to some other possible sources of supply to which attention ims been called, and to continue their investigations of various processes for the purification of the water. One of these processes is an infiltration method of purifying the water of tiie Delaware river opposite the pumping station atLardner’s point, which is only a modification of that pursued at Lawrence, Mass. It is based on the principle that two bodies of water, separated by a bank of material admitting the passage of water through it or through a layer of material underlying both bodies of water, will remain at equal height, if an area were excavated at the side of the Delaware river,protected from the overflow of the river by an embankment the layers of gravel and sand underlying both the river and shore at that point would permit the flow of water from the river to the excavation, filtering it as it passes through these layers. When the excavation is full, the flow will cease, but, as the water is pumped out, it will fill again. The objection to this method is that experience ims shown its impracticability in some cases, owing to the filtrating layers becoming clogged with the matter screened out of tiie water. Such a case occurred in France, where two canals were built side by side, the water passing from one to the other. The filt ration layer soon became impervious to water, and the plant was abandoned. The character of the matter filtered out would have much to do in determining the utility of the method. It isclaimed, however, that this objection does not apply to the conditions at Lardner’s point, since the flow of the river would carry away the matter arrested at the river’s bottom. But it is not altogether certain that this would be the case, as much of the finer matter susI*ended in the water would be carried into the filtrating layer of sand, and must eventually close the passage. It is a question, also, which has not been definitely settled by filtration experts, whether the constant removal of the “bacterial jelly’’ at the surface of the filtration bed by the flow of the river would not destroy the vital element in true filtration.