Shoreline Water District, formerly known as King County Water District No. 42, was officially created by election of the people on August 1, 1931. The first water system facilities were constructed that same year. The water system grew and continued to expand from the 1930’s through the 1960’s as the housing and commercial areas were constructed.

Seattle Public Utilities' (SPU) Cedar River source provided all water supply to the District until 1963. A District pump station, located near NE 185th Street and 5th Avenue NE, was used to pump water into the higher elevations of the District’s water system. This pump station was retired from service and placed on standby in 1963 when Seattle’s Tolt River improvements were completed. The same Tolt River source that started providing the primary supply of water to the District in 1963 is the District’s primary source today. Booster Stations 1 and 2 were constructed in approximately 1963 to pump water into the District’s higher service elevations from the Tolt River pipeline, which was constructed through the middle of the District’s water system.

The construction of I-5 in the mid-1960’s isolated the western part of the District and led to the transfer of some of the District’s customers to Seattle’s direct service area. The only customers on the west side of I-5 that remained within the District’s service area are located north of NE 185th Street. The construction of I-5 also created several areas with dead-end water mains, many of which exist today.

An engineering study that was performed in 1965 identified major deficiencies in the water system, of which the most critical element was the deteriorating old steel water mains. Water system leakage at that time was 27 percent of the purchased supply. The District acted quickly tosolve the problem and replaced most of the old steel water mains and leaking cast iron water mains with new cast iron water mains by the late 1960’s. Prior to making these improvements, customers were charged $4.00 every two months for the first 1,000 cubic feet of water consumed and $0.12 per hundred cubic feet for all water consumed in excess of that. The District implemented a water rate increase to help fund the water main replacement program. The rates were increased to $5.00 per month for the first 600 cubic feet of water consumed and $0.20 per hundred cubic feet for all water consumed in excess of that.

Growth within the District, as well as other nearby areas, continued during the mid-1970’s and water demand increased considerably during that time. Seattle initiated its demand metering program for its wholesale customers, like the District, in the late 1970’s to rectify the impacts on Seattle’s regional system during the summers when peak demands most commonly occurred. This program required the District and other purveyors to build sufficient water storage to supply their systems during peak demand periods and draw a uniform rate of supply from Seattle’s system, or face financial penalties (i.e., Seattle demand charge).

The District implemented several improvements to comply with Seattle’s demand metering program. The 580 Zone 3.7 MG Reservoir was constructed in 1976 and is currently in use and in good condition. A booster pump station was also constructed on the reservoir site to maintain pressures in the higher elevations of the North City area when the reservoir levels were drawn down. Pressure zone boundary adjustments were also implemented about this same time to provide more uniform water pressures to customers.

Specific water main replacements were accomplished during the 1980’s to replace water main that was leaking, failing, or to accommodate improvements of King County or the Washington State Department of Transportation. The District’s 2.0 MG concrete reservoir was constructed in 1988 to provide additional water storage that was needed as a result of the increase in water customers. Other improvements to the District’s system in the 1980’s include rehabilitation of Booster Station 1, piping modifications to the 0.4 MG and 3.7 MG reservoirs, and construction of Pressure Reducing Stations 7, 8, and 9.

Growth within the District during the 1990’s consisted primarily of short platting of larger lots to accommodate additional single family residential homes and the addition of some new multifamily developments. The District completed several water main improvements in the 1990’s to replace old cast iron pipe and increase fire flows. Several other major accomplishments include replacement of Booster Station 2, conversion of the Reservoir Booster Station to the 660 Zone Booster Pump Station, creation of the 660 Zone, installation of two emergency interties with the City of Mountlake Terrace, 3.7 MG Reservoir recoating and access improvements, installation of Pressure Reducing Stations 11 and 12, replacement of Pressure Reducing Station 4, and seismic retrofit of the 3.7MG Reservoir.

The District changed its name in 1991 from King County Water District No. 42 to Shoreline Water District.