WATER WASTE PREVENTION IN NEW YORK CITY
Mr. Bush went into minute details, using many figures, in discussing the immense waste of water in New York Citv, but only a synopsis is here given:
Following a three years’ crusade by the city water department against the waste of water, the consumption was reduced from 525,000,000 gallons per day in 1910 to 186,000,000 gallons at the present time. Allowing tor yearly increase of population, this reduction is equivalent to 90,000,000 gallons daily. This saving was effected at a net cost of $100,000 by means of pitometer surveys, house-to-house inspection and a general educational campaign conducted by the Department of Water Supply, Gas and Electricity. Conditions in Manhattan and the Bronx arc unusually favorabl to the development and continuance of leaks from mains and services outside of buildings without any indication on the surface, in rock-underlaid streets the water main is usually laid in the sewer trench and the filling offers comparatively free passageway for the leaking waters to reach the sewer. Under the above-described conditions leaks amounting to several hundred thousand gallons daily might continue for years without discovery. Numerous leaks of 100,000 gallons daily have been found only after pitometer measurements have shown unreasonably high flows. To simplify the location of these leaks and to reduce the cost of locating them, the department has recently used a “pulsograph,” invented by A. Akinoff, of Philadelphia. This instrument is based upon the water hammer experiments made in Russia in 1897-8 and reported by N. Jonkowsky before the Russian Technical Society April 29, 1898. It consists essentially of a large sensitive pressure recorder having a rapid motion, a tuning fork vibrating at a rate of 200 per second, and a quick-operative valve, which is on a blowoff or by-pass pipe. The instrument is set up by screwing it to a hydrant nozzle, the hydrant being chosen so that there will be a straight run of several hundred feet before an open four-way branch is encountered. By closing valves on intermediate branches, the effect of a long, isolated line can be obtained. In operation the valve on the main below the hydrant is closed and water is allowed to flow from the hydrant through the by-pass on the instrument. By quickly closing the by-pass valve a water hammer of about 15 pounds is created and recorded on the pressure gauge. This pressure is maintained until the water-hammer pressure has reached the open branch at the end of the pipe line that is being tested and the drop in pressure has traveled back to the hydrant, the tuning fork vibrations showing the time for this double travel. By dividing twice the distance along the main to the open branch by the time, the rate of travel for the particular pipe is determined. This has been found to be approximately 3,600 feet per second for 6-inch pipe, increasing to about 4,200 feet for 12-inch pipe. If there is any leak in the main, or in a service near the main, the water-hammer pressure is materially reduced and the chart shows separately the reduction due to the leak and the open branch. The distance to the leak can then be determined by multiplying the time shown on the chart for the water-hammer pressure to travel to the leak and return to the pulsograph by the determined rate of travel of the hammer pressure along the pipe, and dividing by 2. Several leaks have been located within limits of less than 20 feet by the use of this instrument, and the results from its further use should be interesting, as a decided saving in cost of locating leaks is anticipated. One phase of the determination of the need for an additional supply to offset the threatened shortage in 1910-11 was the fixing of the reasonable safe limit of depletion of storage on January 1 of any year. The Rippl, or mass curve method, is usually adopted in determining the safe maximum draft from any watershed. The rule adopted for New York was that the storage should not go below an amount which, added to the lowest runoff recorded for a year, would equal the anticipated consumption for that year. The lowest recorded runoff of the Croton watershed for a calendar year was 207,000,000 gallons daily. With the consumption reduced to 275,000,000 gallons, the deficiency was 68,000,000 gallons daily or 24,820,000,000 gallons in one year. As further reduction could at that time have been made in the consumption, if necessary, the figure of 20,000,000,000 gallons was adopted as the safe reserve supply for New York conditions in 1911; 323,000,000 gallons per day has been adopted as the safe rate of draft. With a gravity supply, which is the condition in Manhattan and the Rronx for about 75 per cent, of the consumption, and with ample aqueduct and reservoir capacity, there is practically no difference in cost between a small and a large use of water, as the same force has to be employed to care for the watershed, reservoirs, aqueduct line and distribution system. The trunk main capacity is, however, affected by the rate of draft, as these mains, in a large, well-designed system, are normally proportioned to the needs for domestic consumption, with some margin for fire purposes. For about every 20,600,006 gallons daily added to the consumption a 48-inch main has to he laid, so that for each 20,000,000 gallons daily saved the laying of a 48-inch main can he eliminated. By taking the average length of trunk main required to deliver water from the end of the aqueduct to the center of distribution and determining the cost of such main, the monetary value of water saved can he arrived at, assuming there is no reason to save water to prevent extensions to the supply system being required, which was the case in Manhattan and the Rronx in 1912. From the terminal of the aqueduct ar 135th street gate house. Manhattan, to the center of distribution is estimated at 25,000 feet. Using a cost of $18 per foot for laying a 48-inch main, the expense would total $450,000. Assuming the canacit” of the 8-inch main to be 20.000,000 gallons daily, the cost per 1,000.000 gallons capacity would he $22,500. Assuming interest, sinking fund and maintenance at 5 1/2 per cent., the cost would he $3.39 per 1,000,000 cmllons. As the lateral distributors in the distribution system are of a capacity based almost entirely on fire-service requirements, there would be no additional saving for such parts of the system, even if the consumption were to he reduced 20 per cent. For the pumped supply the cost of maintenance and operation, including sinking fund on equipment, is equivalent to about $10 per 1,000,000 gallons. From the above it is evident that for the present there is no financial return from reducing water waste where the cost of such saving exceeds $10 per 1,000,000 gallons in districts where the water is pumped and $3.39 per 1,000,000 gallons in districts where the water is delivered by gravity. When the Catskill water supply is introduced and has been utilized to such an extent that pumping from the Brooklyn system will have to be resorted to if waste of water is not curtailed, a very different financial problem will he presented. The work of preventing water waste was in charge of I. M. de Varona, Chief Engineer of the Department of Water, Gas and Electricity of New York City.
No discussion followed the reading of this paper, and the next paper, entitled “The Care and Maintenance of Meters and the Effect on Revenue,” by A. W. Cuddebeck, Superintendent and Engineer Passaic Water Company, was called for and read.