Tap water in Seattle is consistently ranked among the best and cleanest in the nation, meeting or exceeding all federal and state safety standards. Seattle Public Utilities (SPU) achieves this high quality through protected natural sources and robust treatment processes. While the utility delivers excellent water quality up to the property line, residents should be aware that individual home plumbing can introduce localized concerns.
Water Origin: The Seattle Watersheds
Seattle’s water supply originates from two large, protected mountain watersheds. Approximately 70% of the drinking water for the greater Seattle area comes from the Cedar River Watershed, located 35 miles southeast of the city. The remaining 30% is sourced from the South Fork Tolt River Watershed, situated in the foothills of the Cascades.
The source water is primarily fed by rain and snowmelt, collected in reservoirs like Chester Morse Lake and the Tolt Reservoir. Both watersheds are extensively protected, with limited public access and no agricultural, industrial, or recreational activities allowed within their boundaries. This protection plan minimizes the chance of man-made contamination, resulting in source water that is naturally pristine and requires less intensive treatment than many other municipal supplies.
Utility-Level Treatment and Disinfection
SPU employs advanced processes to ensure the water remains safe as it travels to the tap. The treatment protocols differ slightly between the two sources, reflecting the high quality of the raw water. The Cedar River supply is screened to remove debris and then disinfected using a combination of ozone, ultraviolet (UV) light, and chlorination.
The South Fork Tolt River water is also ozonated and disinfected with chlorine, but it additionally undergoes filtration due to its physical characteristics. Both supplies include the addition of lime for pH adjustment, which acts as a corrosion control measure to minimize the leaching of metals from pipes. SPU is responsible for water safety up to the point where the service line connects to a property, complying with the regulations set forth by the Safe Drinking Water Act (SDWA). The Cedar River supply’s high protection has earned it a “Limited Alternative to Filtration” classification from the EPA.
Addressing Local Infrastructure and Lead Concerns
Lead is not present in Seattle’s source water, but it can enter the drinking water through contact with older materials. These materials include lead service lines, lead-based solder used in plumbing installed before 1986, or certain brass fixtures. Homes built before 1930 are most likely to have service lines that could contain lead components, such as a lead gooseneck fitting.
SPU manages corrosion control, which helps form a protective coating inside the pipes to reduce metal leaching. However, homeowners are responsible for the pipes within their property. To reduce potential lead exposure, flush the pipes by running the cold water tap for two minutes if the water has been stagnant for over six hours. Always use cold water for drinking, cooking, and preparing infant formula, as lead dissolves more quickly in hot water. Residents in older homes concerned about their pipes can consider installing point-of-use filters certified to remove lead.
Accessing Official Quality Reports and Home Testing
Seattle Public Utilities publishes an annual Consumer Confidence Report (CCR), which details the results of all water quality testing conducted throughout the year. This report compares the detected levels of contaminants against the standards set by the Environmental Protection Agency (EPA). The CCR is available on the Seattle Public Utilities website, providing transparency on the regulated and unregulated compounds tested.
For residents who want confirmation of their specific home water quality, particularly regarding lead, home testing is the only definitive measure. The Washington State Department of Ecology maintains a database of certified laboratories that can test drinking water, with costs typically ranging from $25 to $50 for analysis. Testing can confirm if localized issues, such as old fixtures or in-home plumbing, are affecting the water quality before it reaches the tap.