At nearly the same grade the water continues on for 2 miles to the Georgetown Reservoir, which has a total capacity of 14,600,000 gallons, an available capacity of 132,700,000 gallons, and a flow line at an elevation of 146 feet. This reservoir, which is approximately half way between the Dalecarlia Reservoir and Georgetown and between the banks of the Potomac River and the Conduit Road, affords a second opportunity for the storage and clarification of the water, and has its walls and banks lined throughout with stone and concrete. The floor and part of the walls of the sedimentation basin are of concrete.

The Preliminary Treatment Plant, which consists of a building for storing the coagulant, the pumps, piping, dissolving tanks, heating plant, and other apparatus for applying the coagulant, is located on the line of the conduit between the Dalecarlia and Georgetown reservoirs at a point just south of the eastern end of the Dalecarlia Reservoir. Here the water is treated with sulphate of alumina during the time of maximum turbidity of the river. This solution is admitted directly into the conduit and thoroughly mixed with the water in the course of its 2-mile travel to the sedimentation basin of the Georgetown Reservoir, where the coagulant and most of the foreign matter is precipitated.

From the Georgetown Reservoir the water flows through a lined tunnel under Washington to the McMillan Park Reservoir, located just south of the U. S. Soldiers' Home Grounds. This tunnel, approximately 10 feet wide, 9 feet high, and 4 miles long, starts at an elevation of 70 57/100 feet at the west connecting shaft of the Georgetown Reservoir, attains a depth of minus 29 45/100 feet under Rock Creek, rises again to an elevation of minus 14 23/100 feet at the east working shaft of the McMillan Park Reservoir and has along its line four shaft for making repairs, cleaning, etc., and three shafts for ventilation.

The McMillan Park Reservoir, total capacity 264,800,000 gallons, available capacity 179,500,000 gallons, with a flow line at 145 feet, is the last of the three reservoirs for the storage of raw water. The banks of this reservoir are lined from the floor to the top with stone. Total water in storage undergoing sedimentation is 630,900,000 gallons, of which amount

453,500,000 gallons, or approximately one week's supply under normal conditions, is available for use.

At the Washington Filtration Plant the water is lifted from that reservoir about 21 feet by means of three Worthington centrifugal pumps, each with a daily capacity of 40,000,000 gallons, directly connected to Harrisburg engines installed in the Pumping Station, and distributed to the 29 filter beds, each with a filter area of 1 acre. Here the water is filtered by the slow sand method. The water, settling through 4 feet of sand and gravel, is clarified of its impurities and sediment and then flows by gravity to the filtered-water reservoir in the Filtration Plant, flow line at 162 feet. This reservoir, like the filter beds, is entirely covered with earth over a groined-arched concrete roof and has a total capacity of 15,000,000 gallons, all of which is available. Besides the Pumping Station at the Washington Filtration Plant, there is also a sand-washing and storage system, a laboratory for testing water, and the necessary piping and valves for carrying the water and controlling the rates of filtration.

The filtered water now passes under the McMillan Park Reservoir through four 48-inch cast-iron pipes to the East Shaft Gate House on the west side of the reservoir, where the flow line is reduced to 147 feet above mean tide by means of controlling valves in the outlet mains from the filtered-water reservoir.

Up to this point the water, conduit, tunnel, reservoirs, purification plant, and everything pertaining to the supply and purification systems is the property of the United States Government and is under the supervision of the U. S. Engineer Corps, but from here on the water and all the properties pertaining to its distribution are owned by the District of Columbia, and are under the care of the Water Department.

Fifty-five and five-tenths per cent of the water flows by gravity through two 48-inch cast-iron trunk mains directly to the service water mains which supply the consumers in those parts of the city having ground elevations between 0 and 70 feet above mean tide level. The balance of the water flows by gravity through two 48-inch cast-iron trunk mains to the District Pumping Station, located on Bryant Street, N. W., between

2d and 4th Streets and just south of the McMillan Park Reservoir, where it is pumped to the higher elevations of the District. Daily average consumption of the gravity service is 30,453,000 gallons. The maximum pressure for this service is 60 pounds per square inch, the minimum pressure is 26 pounds per square inch, and the general pressure is between 45 and 50 pounds per square inch.

The pumped area is divided into the first high, second high, third high, and fourth high services, which supply those portions of the District west of the Anacostia River between the elevations of 70 and 140 feet, 140 and 210 feet, 210 and 350 feet, and 350 and 423 feet respectively.

The first high service is direct pumpage. There are no reservoirs on this service, the supply being controlled by automatic governing devices on the pumps to give a constant hydraulic head of 210 feet above mean tide level. Two pumping engines, each with a capacity of 20,000,000 gallons in 24 hours, supply the first high service; 31 33/100 per cent of the total filtered water goes to this service through a 48-inch cast-iron trunk main. Daily average consumption of the first high service is 17,332,000 gallons. Maximum pressure 65 pounds per square inch, minimum pressure 26 pounds per square inch, general pressure between 50 and 55 pounds per square inch.

The second high service is pumped through a 36-inch cast-iron trunk main to the Brightwood Reservoir, an equalizing reservoir with concrete floor and walls, having a capacity of 30,000,000 gallons, all of which is available, and a flow line at 276 feet. One pumping engine, capacity 12,000,000 gallons in 24 hours, supplies the second high service; 9 95/100 per cent of the total water goes to this service. Daily average consumption of the second high service is 5,506,000 gallons. Maximum pressure on this service is 81 pounds per square inch, minimum pressure 22 pounds per square inch, general pressure 40 pounds per square inch.

The third high service is pumped to the Reno Reservoir. This reservoir is similar in its functions and construction to the Brightwood Reservoir, and has a total available capacity of 4,500,000 gallons, with a flow line at 423 feet. One pumping engine, with a capacity of 2,500,000 gallons in

24 hours, supplies the third high service; 2 91/100 per cent of the total water is pumped to this service and is supplied through two 12-inch cast-iron trunk mains reduced from a 30-inch and a 20-inch main. Daily average consumption of the third high service is 1,607,000 gallons. The maximum pressure is 117 pounds per square inch, minimum pressure 24 pounds per square inch, general pressure between 50 and 60 pounds per square inch. There is one pumping engine, capacity 5,000,000 gallons in 24 hours, used as an auxiliary engine for the second and third high services.

Part of the water of the Reno Reservoir is lifted by means of auxiliary pumps, located at the reservoir in the Reno Pumping Station, to a steel tank in the Reno Tower, capacity 83,500 gallons, flow line at 485 feet. The water thus used constitutes the fourth high service and serves a territory of about 1 square miles, constituting the highest ground in the District, through a 12-inch cast-iron trunk main. About 28/100 per cent of the total water goes to this service. Daily average consumption of the fourth high service is 152,000 gallons. The maximum pressure taken at the street level on fire hydrants is 69 pounds per square inch, minimum pressure is 28 pounds per square inch, and the general pressure is 40 pounds per square inch.

The gravity service from the city also supplies a portion of the territory east of the Anacostia River, lying between elevations of 0 and 70 feet through a 70-inch cast-iron trunk main. The maximum pressure on this service taken at the street level on fire hydrants is 50 pounds per square inch, the minimum pressure is 19 pounds per square inch, and the general pressure between 40 and 45 pounds per square inch.

Besides the gravity service, there were created in July, 1913, two new pumped services, which are termed the first and second high services, Anacostia, D. C. The water flows by gravity from the city to the Anacostia Pumping Station, situated at 18th Street and Minnesota Avenue, S. E. From here the first high service is pumped through 20-inch and 12-inch cast-iron trunk mains to two steel water towers with a capacity of 140,000 gallons each, one located at 13th and R streets, S. E., and the

other at 11th Place and Alabama Avenue, S. E., each having a flow line of 246 feet. These two towers serve that area lying between the elevations of 70 and 170 feet above mean tide. About 48/100 per cent of the total water goes to this service. Daily average consumption of the first high service is 267,000 gallons. The maximum pressure taken at the street level on fire hydrants is 91 pounds per square inch, minimum pressure 19 pounds per square inch, and the general pressure between 40 and 55 pounds per square inch.

The second high service is pumped through a 12-inch cast-iron trunk main to a third steel water tower with a capacity of 140,000 gallons and flow line at 350 feet, situated on the Stanton School Grounds, 25th Street south from Good Hope Road, S. E. This tower supplies that area lying between the elevations of 170 and 310 feet, the highest ground in the District east of the Anacostia River. Daily average consumption of the second high service is small at the present time, and is included in the figure of the first high service, Anacostia, D. C. The maximum pressure taken at the street level on the fire hydrants is 103 pounds per square inch, the minimum pressure 32 pounds per square inch.

STATISTICAL

Ownership: Supply, U. S. Government under U. S. Engineer Corps. Distribution, Water Department of District of Columbia.

Source: Potomac River at Great Falls.

Fire Hydrants: 3166.

Mains.

Length, miles: 574.

Diameter, inches: 3 to 75.

Pressure.

House, lbs.: 22 to 117.

Fire, lbs.: 22 to 117.

Daily capacity of pumps, gallons: 120,000,000.

Daily consumption, gallons: 57,282,000.

Percentage of population supplied: 100.

Reserve storage: 630,900,000 gallons.