=Pure-water Reservoir.=—A small pure-water reservoir, 94 feet square and holding about 600,000 gallons, is provided at the filter-plant. The construction is similar to that of the filters, but the shapes of the piers and vaulting were changed slightly, as there was no necessity for the ledges about the bottoms of the piers and walls; while provision is made for taking the rain-water, falling upon the vaulting above, to the nearest filters instead of allowing it to enter the reservoir. The floor and roof of the reservoir are at the same levels as those of the filters. CAPACITY OF PLANT AND MEANS OF REGULATION. The various filters have effective filtering areas of from 0.702 to 0.704 acre, depending upon slight differences in the thickness of the walls in different places. For the purpose of computation, the area of each filter is taken at 0.7 acre. The nominal rate of filtration is taken as 3,000,000 gallons per acre daily, at which rate each filter will yield 2,100,000 gallons daily, and, with one filter out of use for the purpose of being cleaned, seven filters normally in use will yield 14,700,000 gallons. The entrances and outlets are all made of sufficient size, so that rates 50 per cent greater than the foregoing are possible. The capacities of the intake, pumping-station, and piping are such as to supply any quantity of water which the filters can take, up to an extreme maximum of 25,000,000 gallons in 24 hours. The pure-water conduit from the filters to Quackenbush Street is nominally rated at 25,000,000 gallons per 24 hours, after it has become old and somewhat tuberculated. In its present excellent condition it will carry a larger quantity, At the pumping-station at Quackenbush Street there are three Allis pumps, each capable of pumping 5,000,000 gallons per 24 hours. In addition to the above there are the old reserve pumps with a nominal capacity of 10,000,000 gallons per 24 hours, which can be used if necessary, but which require so much coal that they are seldom used. For practical purposes the 15,000,000 gallons represents the pumping capacity of this station and also the capacity of the filters, but the arrangements are such that in case of emergency the supply can be increased to 20,000,000 or even 25,000,000 gallons for a short time.