What Seattle Residents Should Know
Seattle's drinking water comes primarily from two protected mountain watersheds: the Cedar River Watershed and the South Fork Tolt River Watershed in the Cascade Mountains. Seattle Public Utilities (SPU) owns and manages these watersheds, limiting human access and development to maintain exceptionally high source water quality.
The pristine nature of these sources means Seattle's water requires minimal treatment compared to many other U.S. cities. The water is filtered (at the Tolt source) or undergoes ozonation (at the Cedar source), then is disinfected, pH adjusted, and fluoridated before distribution to approximately 1.5 million people in the greater Seattle area.
Despite this high-quality source water, Seattle faces two main challenges. First, like many older cities, Seattle has neighborhoods with lead service lines or lead plumbing components in buildings constructed before 1986. Second, the city is engaged in ongoing infrastructure upgrades to replace aging pipes and facilities, which can occasionally cause temporary water quality fluctuations in specific neighborhoods.
Key Contaminants Found
These substances have been detected in Seattle's water supply, though most are at levels well below regulatory limits.
Lead
Below LimitSource: Lead service lines, lead solder in plumbing, and older fixtures in pre-1986 buildings
Health Effects: Developmental delays in children, learning disabilities, reduced IQ, kidney problems, high blood pressure
Seattle Levels: Average 2.8 ppb (90th percentile), with less than 2% of samples exceeding the EPA action level
EPA Limit: Action level 15 ppb, but no safe level exists
Total Trihalomethanes (TTHMs)
Well Below LimitSource: Byproducts formed when chlorine used to disinfect water reacts with organic matter
Health Effects: Potential increased risk of cancer with long-term exposure, liver and kidney problems
Seattle Levels: 15-25 ppb, varying by location, among the lowest in major U.S. cities
EPA Limit: 80 ppb
Soft Water Minerals
Not a Health ConcernSource: Natural mineral content from the mountain watersheds
Health Effects: No health concerns; Seattle's very soft water actually requires pH adjustment to prevent pipe corrosion
Seattle Levels: 1.5 grains per gallon (25.7 mg/L), considered "very soft"
EPA Limit: Not regulated (aesthetic characteristic only)
Fluoride (Added)
Optimal LevelSource: Added during water treatment for dental health benefits
Health Effects: Beneficial for dental health at current levels; Seattle maintains fluoride at optimal concentrations
Seattle Levels: 0.7 ppm, the recommended level for dental health
EPA Limit: 4.0 ppm (much higher than Seattle's target level)
Neighborhood Variations
Water quality can vary across Seattle's diverse neighborhoods, primarily due to differences in building age and infrastructure.
Water Quality by Area
| Neighborhood/Area | Risk Level | Water Source | Buildings Pre-1986 | Notable Concerns |
|---|---|---|---|---|
| Capitol Hill/First Hill | Medium | Cedar River | 80% | Lead, Aging Infrastructure |
| Central District/International District | Medium | Cedar River | 75% | Lead, Aging Infrastructure |
| Queen Anne/Magnolia | Medium | Cedar River | 72% | Lead |
| Ballard/Fremont | Low | South Fork Tolt | 60% | Minimal Concerns |
| West Seattle | Low | Cedar River | 55% | Minimal Concerns |
| North Seattle | Low | South Fork Tolt | 45% | Minimal Concerns |
Data based on Seattle Public Utilities sampling and building age estimates.
Recommended Action Steps
While Seattle's water is generally of excellent quality, these actions can further protect your household, particularly in older buildings.
Test Your Water If in a Historic Building
If you live in a pre-1986 building, especially in Capitol Hill, First Hill, or the Central District, consider testing your water for lead. Seattle Public Utilities offers free lead testing kits for residents.
Free Lead Testing ProgramRun Cold Water Before Use
In older buildings, run cold water for 30-60 seconds before using it for drinking or cooking, especially in the morning or after being away from home for several hours. This helps flush out any lead that may have leached into water sitting in pipes.
Check for Lead Plumbing
If you live in an older building, check your service line material and interior plumbing for lead components. Seattle Public Utilities maintains records for many properties and can help you identify if you have lead service lines or goosenecks.
Lead Plumbing InformationConsider Simple Filtration
While Seattle's water is already of excellent quality, a simple carbon filter can further improve taste and provide additional peace of mind, particularly for households with children or pregnant women in older buildings where lead is a concern.
Stay Informed About Infrastructure Work
Seattle Public Utilities is constantly upgrading water infrastructure throughout the city. Sign up for notifications about work in your neighborhood, as construction can occasionally cause temporary changes in water appearance or pressure.
Neighborhood ProjectsSupport Watershed Protection
Seattle's excellent water quality begins with its protected watersheds. Support local initiatives to maintain and protect these critical natural resources, which are among the most pristine municipal water sources in the United States.
Watershed InformationWant to know your personal water quality risk?
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