HOW COMMUNITIES OBTAIN PURE WATER 



65 



of Manhattan Island (area, 22 sq. mi.) to a depth of 

 thirty feet. Water from this reservoir is taken through 

 ninety-two miles of aqueduct to the five boroughs of 

 the city, where it is stored in large reserve reservoirs 

 until needed. The map shows the Esopus watershed 

 and the Ashokan reservoir connected to the city by 

 the Catskill tunnel. Study the map carefully. Figure 

 103 shows a picture of the Ashokan reservoir. 



Board of H'atrr Supply, Kcm York Citv 

 FIG. 102. MAP OF NEW YORK WATER SUPPLY SYSTEM 



The Catskill aqueduct which conducts the water 

 from the Ashokan reservoir to the Kensico reservoir 

 varies from fourteen to seventeen feet in diameter. 

 Where this aqueduct goes under the Hudson River it 

 was tunneled through solid rock at a depth of 1,100 

 feet below sea level. This great tunnel is capable of 

 carrying 600,000,000 gallons of water to the city daily. 

 The Esopus watershed supplies about 300,000,000 gal- 

 lons a day. 



To provide for recent growth of the city the great 

 Schoharie watershed to the north of the Esopus area 

 has been developed. This watershed contains about 

 314 square miles and is drained by Schoharie Creek, 

 which flows northward into the Mohawk River. To 

 change the flow of this creek a great dam has been 

 built at Gilboa. This backs the water up so that it may 

 be conducted by tunnel to Esopus Creek and then into 

 the Ashokan reservoir. This great watershed is also 

 capable of supplying upwards of 300,000,000 gallons 

 of water daily. 



In general the water supplied to New York City 

 is very pure and requires only a limited amount of 

 treatment. Just below the Ashokan reservoir pro- 

 vision has been made for jetting the water into the 



Courtesy Board of Water Stiffly, AYjt' York City 



FIG. 103. ASHOKAN RESERVOIR 



air through about 1,600 nozzles. This process, called 

 aeration, serves to mix the water thoroughly with the 

 oxygen of the air, killing some bacteria and removing 

 certain objectionable gases. This process is repeated 

 at the Kensico dam. The water is also sterilized 1 with 

 chlorine, thus assuring that most of the bacteria are 

 killed. At times of heavy rainfall in some of the reser- 

 voirs the water becomes somewhat cloudy. Aluminum 

 sulphate and soda ash are then added to settle the 

 suspended matter more quickly. The water supplied 

 in the New York area is very soft and frequently very 

 active on iron pipes, causing them to rust rapidly. 



This great water supply system is one of the best 

 examples of how community health is guarded by 

 pure water. It also illustrates the tremendous engi- 

 neering problems that must frequently be solved be- 

 fore pure water may be supplied. 



The city of St. Louis is located on the Mississippi 

 River, about fifteen miles south of its junction with 

 the Missouri River. The older part of the water sup- 

 ply system, known as the Chain of Rocks plant, is 

 located on the Mississippi River about five miles 



1 Sterilized, made free from harmful bacteria. 



