0.33 | 1.75 | 39.0 | 2,400
16 | 0.33 | 1.78 | 42.3 | 3,000
17 | 0.33 | 1.86 | 45.5 | 3,300
18 | 0.34 | 1.80 | 48.7 | 3,100
19 | 0.34 | 1.80 | 52.0 | .....
20 | 0.34 | 1.87 | 39.0 | 2,700
21 | 0.32 | 1.82 | 42.3 | 2,400
22 | 0.33 | 1.74 | 45.5 | 2,200
23 | 0.33 | 1.81 | 48.7 | 2,300
24 | 0.35 | 1.80 | 52.0 | 2,600
25 | 0.29 | 1.64 | 39.5 | 2,400
26 | 0.31 | 1.71 | 37.1 | 2,100
27 | 0.31 | 1.71 | 34.7 | 1,900
28 | 0.33 | 1.93 | 33.6 | 2,300
29 | 0.34 | 1.93 | 33.6 | 3,000
-------+---------------+------------+--------+----------
Maximum| 0.36 | 1.93 | 52.0 | 3,300
Minimum| 0.29 | 1.64 | 33.6 | 1,800
Average| 0.32 | 1.77 | 40.4 | 2,600
=======+===============+============+========+==========

_Description of Washington Aqueduct._--The water supply of
Washington is taken from the Potomac River, at Great Falls, about 16
miles above the city. At that place, a dam has been built across the
river, which holds the water at an elevation of 150.5 ft. above mean
tide at Washington. From Great Falls the water flows by gravity for
a distance of 16 miles through a 9-ft. conduit, three reservoirs,
and a tunnel. From McMillan Park Reservoir, the last of the three,
the water is lifted by centrifugal pumps about 21 ft. to the
filters. After passing through the filters, it flows to the
filtered-water reservoir, and later to the city mains. In its
passage from Great Falls to the filters, the water flows through
three settling reservoirs, which have already been referred to.
These reservoirs are known as the Dalecarlia, the Georgetown, and
the McMillan Park Reservoirs, and have available capacities of
141,000,000, 140,000,000, and 180,000,000 gal., respectively.

_Turbidity._--The Potomac River water is rather turbid, the
turbidity being caused by very fine particles of clay. The river is
subject to sudden fluctuations, it being no uncommon thing to have a
turbidity of 100 one day, and 1,000 the next. The high turbidity
usually disappears about as rapidly as it comes, and is seldom
higher than 500 for more than 5 days at a t