Water System

The City owns its water supply system, fed by two pristine reservoirs in the Cascade Mountains. From 1910 to 1997, the Water Department oversaw the water system before the agency’s absorption by Seattle Public Utilities. The Engineering Department constructed, and the Department of Streets and Sewers managed, Seattle's drainage and sewage infrastructure from 1896 to 1936. The Engineering Department assumed sole management from 1936 to 1997 (except for the transfer of sewage treatment facilities to METRO in 1961), and Seattle Public Utilities took over in 1997.

Water Supply

After the Great Fire of 1889, citizens voted to fund the creation of a municipally-owned water system. The City purchased private suppliers that drew primarily on Lake Washington and ground water sources. As these sources became increasingly inadequate and unsanitary, Seattleites financed the purchase of the upper Cedar River Watershed and construction of a gravity-powered water transport and storage facilities. Fifty years later, demand exceeded Cedar River supply, and the City purchased and built a second Cascades supply in the Tolt River Watershed. Seattle supplies fresh water to over 1.35 million people in the greater metropolitan area, either directly or through surrounding cities and water districts.

Cedar River Pipeline under construction
Cedar River Pipeline No. 1
under construction on hill
east of Renton, 1899
Seattle built a 28.5 mile pipeline
that delivered Cedar River water
to the Volunteer Park and
Lincoln Reservoirs on Capitol Hill.
Seattle Municipal Archives Image 7261
water testing lab
City Water testing laboratory, 1948
Seattle Municipal Archives Image 41114
Masonry Dam
Aerial of Masonry Dam, 2009
The Masonry Dam diverts water
from Masonry Pool to the City Light
plant 620 feet below at Cedar Falls
for hydroelectric generation.
Seattle Municipal Archives Image 162834

In-City Facilities

Seattle built and maintains an extensive network of pipelines and water mains, tunnels, reservoirs, and water towers within the city limits and in adjoining suburban communities to the north and south.

Lincoln Park pumping station
Lincoln Park pumping station, 1929
Seattle Municipal Archives Image 6911
Volunteer Park water tower
Standpipe and gate house
in Volunteer Park, 1910
Seattle Municipal Archives Image 52058
water main replacement
Replacing wooden water main with
concrete on Federal Avenue, 1957
Seattle Municipal Archives Image 54263

Sewers and Drainage

Prior to 1890, Seattle relied on a haphazard assortment of sewers and cesspools that, at best, drained into surrounding lakes and salt water. Faced with recurring threats of waterborne diseases including typhoid and cholera, City Engineer Benezette Williams designed the Seattle's first centralized combined sewage system plan in 1891. This plan sought to remove as much city sewage as possible into the salt water of Elliott Bay and the Puget Sound with more limited drainage into the fresh water of Lake Washington. Although originally untreated, the City undertook a succession of steps starting in the late 1910's to remove solids, begin primary sewage treatment, and eventually separate storm water from raw sewage. Metropolitan King County took over the City's wastewater treatment responsibilities in the 1960's, but Seattle continues to manage its network of storm sewers.

north trunk sewer siphon tunnel
North trunk sewer siphon tunnel, 1913
Seattle Municipal Archives Image 6229
Holly Street outfall
Holly Street Outfall extended
into Lake Washington, 1930
Seattle Municipal Archives Image 47035
water treatment plant
Lake City water treatment plant, 1955
Seattle Municipal Archives Image 52379
sewer break
Sewer break at 5th & Washington, 1921
Seattle Municipal Archives Image 12950

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