Is Mercer Island, WA Tap Water Safe to Drink?
Graded A-, with 3 unresolved violations on record. See what was cited — and what it means for your tap. What to do next ↓
86.8/100
waterverge.com Mercer Island, WA — Water Quality Report
Mercer Island's drinking water received a grade of A- (86.8 out of 100), indicating good water quality. The city's 2 water systems serve approximately 30,785 residents using purchased surface water.
Lead levels were measured at 6.3 ppb (90th percentile), which is within EPA limits but above recommended levels. PFAS testing under UCMR 5 found no detectable forever chemicals.
The system has 12 violations on record, including 1 health-based violation. 3 remain unresolved.
What to know about Mercer Island's water
Mercer Island ranks #80 out of 294 cities in Washington for water quality, placing it mid-range in the state.
The city draws from surface water sources, which are more susceptible to seasonal runoff and agricultural contamination, requiring extensive multi-barrier treatment including coagulation, filtration, and disinfection.
Hexavalent chromium (chromium-6) was detected at 0.17 µg/L in UCMR 3 testing. While below California's 10 µg/L limit and with no federal MCL set, residents sensitive to this contaminant may consider reverse osmosis filtration.
While lead levels are within EPA limits, they are above the recommended 5 ppb threshold that health organizations consider ideal. A point-of-use filter adds an extra layer of protection.
Water quality score
See methodology →Is Mercer Island, WA water safe to drink?
Mercer Island's drinking water has significant quality concerns based on EPA testing data. With a grade of A- (86.8/100), the system has issues across multiple categories. A water filter is recommended for all residents. The city's 2 water systems serve approximately 30,785 residents using surface water (rivers, lakes, or reservoirs).
Recent water quality updates for Mercer Island
A timeline of significant water quality events, violations, and data updates.
Latest EPA compliance and testing data incorporated into Mercer Island's water quality assessment. Grade: A- (86.8/100).
Federal disaster declaration (FEMA DR-3629). Flood event — may have impacted local water infrastructure.
Federal disaster declaration (FEMA DR-4539). Flood event — may have impacted local water infrastructure.
Contaminants: Consumer Confidence Rule.
Contaminants: Coliform (TCR).
Contaminants: Lead and Copper Rule.
Key contaminant findings
Based on the most recent EPA sampling data for Mercer Island's water supply.
Within EPA limits but above the American Academy of Pediatrics recommended level of 1 ppb. An NSF 53-certified filter provides additional protection.
Violation history
Mercer Island's water system has 12 total violations on record, including 1 health-based violation. 3 remain unresolved.
Flood & environmental risk
King County has experienced 10 federally declared disasters since 1990. Flooding and severe storms can overwhelm water treatment plants, cause sewage overflows, and introduce agricultural runoff, bacteria, and sediment into drinking water supplies. Local water sources include Springbrook Creek, Mill Creek, Green River, Duwamish River, Duwamish R.
Where does Mercer Island's water come from?
Mercer Island's drinking water comes from surface water (rivers, lakes, or reservoirs), supplied by 2 water systems serving approximately 30,785 people. Surface water sources are more susceptible to contamination from runoff, industrial discharge, and algal blooms, requiring extensive treatment. Nearby water bodies include Springbrook Creek (river), Mill Creek (river), Green River (river), Duwamish River (river), Duwamish R (river).
What Mercer Island residents can do
Recommended: NSF-certified water filter. This addresses the specific contaminants found in Mercer Island's water.
Your water utility is required to publish an annual Consumer Confidence Report (CCR) with detailed testing results. Ask for the latest copy or check your utility's website.
Run cold water for 30 seconds before drinking, especially in the morning. Lead and copper leach from household plumbing when water sits in pipes.
Mercer Island's area has a history of flooding. After severe weather, watch for boil water advisories from your local utility.
Data: EPA SDWIS, UCMR 5 (PFAS), FEMA, NOAA. Last updated May 2026.
Top contaminants to know
View all ↓Forever chemicals overview
National PFAS report →Violation summary
Violations & advisories
Top industrial polluters within 10 miles of Mercer Island
Industrial polluters nearby
Reported releases to surface water by facilities near Mercer Island, ranked by pounds discharged annually.
Total reported releases to surface water: 129 lbs
| Facility | Top chemical | To surface water (lbs/yr) | Distance |
|---|---|---|---|
DAVIS WIRE CORP KENT, WA98032 | Lead compounds | 108 | 9.4 mi |
NUCOR STEEL SEATTLE INC SEATTLE, WA98106 | Zinc compounds | 11 | 6.2 mi |
ACE GALVANIZING INC SEATTLE, WA98108 | Zinc compounds | 5 | 5.6 mi |
BOEING COMMERCIAL AIRPLANE GROUP - RENTON RENTON, WA98055 | Copper | 3 | 4.7 mi |
TEREX WASHINGTON SOUTH CAMPUS REDMOND, WA98052 | Certain glycol ethers | 2 | 9.5 mi |
Source: EPA Toxic Release Inventory (TRI) 2023
Superfund sites within 10 miles of Mercer Island
Superfund sites nearby
Federally tracked hazardous-waste sites on the EPA National Priorities List. Proximity does not necessarily indicate tap-water contamination — the connection depends on hydrology and treatment.
- QUENDALL TERMINALS2.6 mi
- LOWER DUWAMISH WATERWAY4.7 mi
- PACIFIC CAR FOUNDRY CO5.4 mi
- HARBOR ISLAND LEAD5.7 mi
- LOCKHEED WEST SEATTLE6.3 mi
+ 2 more sites
Source: EPA Superfund National Priorities List
Flood & disaster history
King County has experienced 10 federally declared disasters since 1990. Flooding and severe weather can compromise water treatment infrastructure and introduce contaminants into drinking water supplies.
Recommended water filters
Based on contaminants detected in Mercer Island's water supply, we recommend the following filter types.
Full contaminants report
| Contaminant | Detected Level | EPA Limit | Unit | Category | Status |
|---|---|---|---|---|---|
| Lead (90th percentile) LeadHeavy Metal A toxic heavy metal that can leach into drinking water from older pipes, solder, and fixtures. No amount of lead in water is considered safe. Health EffectsBrain and nervous system damage in children, kidney damage, high blood pressure, and reproductive problems in adults. EPA Limit15 ppb action level Common SourcesCorrosion of lead pipes, lead solder, brass faucets, and household plumbing. | 6.3 | 15 | ppb | Inorganic | Safe |
| 11Cl-PF3OUdS | ND | HI | µg/L | PFAS | Not Detected |
| 4:2 FTS | ND | HI | µg/L | PFAS | Not Detected |
| 6:2 FTS 6:2 FTSPFAS A fluorotelomer sulfonate commonly found at sites contaminated with aqueous film-forming foam (AFFF) used in firefighting. Health EffectsPotential liver toxicity and endocrine disruption. Less studied but identified as a contaminant of concern. EPA LimitNo individual MCL (not yet regulated) Common SourcesFirefighting foam (AFFF), airports, military bases, and industrial facilities. | ND | HI | µg/L | PFAS | Not Detected |
| 8:2 FTS | ND | HI | µg/L | PFAS | Not Detected |
| 9Cl-PF3ONS | ND | HI | µg/L | PFAS | Not Detected |
| ADONA | ND | HI | µg/L | PFAS | Not Detected |
| HFPO-DA HFPO-DA (GenX)PFAS A replacement for PFOA in manufacturing, marketed as safer but still a persistent "forever chemical." Also known as GenX. Health EffectsLiver and kidney effects, reproductive toxicity, immune system effects, and potential cancer risk. EPA Limit10 ppt MCL Common SourcesFluoropolymer manufacturing (used as PFOA replacement), industrial wastewater discharge. | ND | 0.01 | µg/L | PFAS | Not Detected |
| lithium LithiumInorganic A naturally occurring alkali metal found in groundwater. Monitored under UCMR 5 to assess occurrence in drinking water. Health EffectsKidney effects at high doses. Low-level exposure effects under study; some research suggests neurological effects. EPA LimitNo MCL (monitoring only under UCMR 5) Common SourcesNatural mineral deposits, geothermal water, and industrial discharge. | ND | HI | µg/L | PFAS | Not Detected |
| NEtFOSAA | ND | HI | µg/L | PFAS | Not Detected |
| NFDHA | ND | HI | µg/L | PFAS | Not Detected |
| NMeFOSAA | ND | HI | µg/L | PFAS | Not Detected |
| PFBA PFBAPFAS One of the shortest-chain PFAS compounds. Very mobile in water and difficult to remove with standard filtration. Health EffectsThyroid effects, potential developmental toxicity. Shorter half-life in body than long-chain PFAS. EPA LimitNo individual MCL (not yet regulated) Common SourcesDegradation of longer-chain PFAS, industrial discharge, and firefighting foam. | ND | HI | µg/L | PFAS | Not Detected |
| PFBS PFBSPFAS A short-chain PFAS used as a replacement for PFOS. While it clears the body faster than long-chain PFAS, it still persists in the environment. Health EffectsThyroid effects, reproductive and developmental toxicity, kidney effects. EPA LimitPart of Hazard Index (1.0) Common SourcesIndustrial discharge, firefighting foam, and as a replacement chemical in manufacturing. | ND | HI | µg/L | PFAS | Not Detected |
| PFDA | ND | HI | µg/L | PFAS | Not Detected |
| PFDoA | ND | HI | µg/L | PFAS | Not Detected |
| PFEESA | ND | HI | µg/L | PFAS | Not Detected |
| PFHpA PFHpAPFAS A medium-chain PFAS compound found in various environmental samples. Less studied than PFOA/PFOS but still considered a contaminant of concern. Health EffectsLiver effects, potential developmental toxicity, and endocrine disruption. EPA LimitPart of Hazard Index (1.0) Common SourcesDegradation of longer-chain PFAS, industrial discharge, and contaminated water sources. | ND | HI | µg/L | PFAS | Not Detected |
| PFHpS | ND | HI | µg/L | PFAS | Not Detected |
| PFHxA PFHxAPFAS A short-chain PFAS replacement chemical widely used after manufacturers phased out longer-chain PFAS. Very commonly detected in water. Health EffectsLiver and kidney effects, potential thyroid disruption. Considered less toxic than long-chain PFAS but still persistent. EPA LimitNo individual MCL (not yet regulated) Common SourcesIndustrial processes, firefighting foam (AFFF), food packaging, and textile treatment. | ND | HI | µg/L | PFAS | Not Detected |
| PFHxS PFHxSPFAS A medium-chain PFAS found in firefighting foam and consumer products. It has a long half-life in the human body, similar to long-chain PFAS. Health EffectsImmune system effects, thyroid disruption, and potential reproductive and developmental harm. EPA LimitPart of Hazard Index (1.0) Common SourcesFirefighting foam (AFFF), waterproof textiles, food packaging, and industrial discharge. | ND | HI | µg/L | PFAS | Not Detected |
| PFMBA | ND | HI | µg/L | PFAS | Not Detected |
| PFMPA | ND | HI | µg/L | PFAS | Not Detected |
| PFNA PFNAPFAS A long-chain PFAS compound used in manufacturing fluoropolymers. It bioaccumulates in the body and is very persistent in the environment. Health EffectsDevelopmental effects, liver toxicity, immune suppression, and potential cancer risk. EPA LimitPart of Hazard Index (1.0) Common SourcesFluoropolymer manufacturing, industrial emissions, and contaminated water sources. | ND | HI | µg/L | PFAS | Not Detected |
| PFOA PFOAPFAS A long-chain PFAS ("forever chemical") once widely used in nonstick coatings and firefighting foam. It persists in the body and environment for years. Health EffectsLinked to kidney and testicular cancer, thyroid disease, elevated cholesterol, and reproductive issues. EPA Limit4.0 ppt MCL Common SourcesIndustrial discharge, firefighting foam (AFFF), nonstick cookware manufacturing, and contaminated groundwater. | ND | 0.004 | µg/L | PFAS | Not Detected |
| PFOS PFOSPFAS A long-chain PFAS compound historically used in stain-resistant coatings and firefighting foam. One of the most studied and persistent PFAS chemicals. Health EffectsLiver damage, immune system suppression, thyroid disruption, increased cholesterol, and potential cancer risk. EPA Limit4.0 ppt MCL Common SourcesFirefighting foam (AFFF), industrial sites, stain-resistant fabric treatments, and contaminated groundwater. | ND | 0.004 | µg/L | PFAS | Not Detected |
| PFPeA PFPeAPFAS A short-chain PFAS compound commonly detected in drinking water. One of the most frequently found PFAS in UCMR 5 monitoring. Health EffectsLess studied than PFOA/PFOS. Potential liver and thyroid effects. Research is ongoing. EPA LimitNo individual MCL (not yet regulated) Common SourcesIndustrial discharge, firefighting foam degradation, and consumer products. | ND | HI | µg/L | PFAS | Not Detected |
| PFPeS | ND | HI | µg/L | PFAS | Not Detected |
| PFTA | ND | HI | µg/L | PFAS | Not Detected |
| PFTrDA | ND | HI | µg/L | PFAS | Not Detected |
| PFUnA | ND | HI | µg/L | PFAS | Not Detected |
Lead level trend (90th percentile)
See how Mercer Island compares by contaminant
Explore where Mercer Island ranks among all Washington cities for specific contaminants.
Water source & infrastructure
Where Mercer Island's water comes from
Mercer Island's drinking water comes primarily from surface water sources such as rivers, lakes, or reservoirs.
Surface water systems require multi-stage treatment including coagulation, sedimentation, filtration, and disinfection to meet EPA Safe Drinking Water Act standards.
These sources can be impacted by seasonal changes, stormwater runoff, upstream agriculture, and industrial discharge.
The system is operated by local government ownership and serves approximately 30,785 people through 2 water systems.
Water bodies near Mercer Island
Mercer Island is located near 5 notable water bodies. As a surface water system, these water bodies may directly influence the city's drinking water supply.
Water systems serving Mercer Island
| System Name | PWSID | Population | Source |
|---|---|---|---|
| MERCER ISLAND CITY OF | WA5353640 | 30,689 | SWP |
| SPRING GLEN MOBILE HOME PARK | WA5383290 | 96 | GW |
How Mercer Island compares
Full Washington rankings →Mercer Island's score of 86.8/100 is above the average of 53/100 among major Washington cities. It outscores 9 of 10 nearby cities.
Nearby cities
View Washington rankings →About Mercer Island, WA
Wikipedia →Mercer Island is a city in King County, Washington, United States, located on an island of the same name in the southern portion of Lake Washington. Mercer Island is in the Seattle metropolitan area, connected to the mainland on both sides by bridges carrying Interstate 90, with the city of Seattle to the west and the city of Bellevue to the east.
Learn more about your water
Guides and resources related to Mercer Island's water quality findings.
Explore water quality across King
Frequently asked questions
Is Mercer Island, WA tap water safe to drink?
Mercer Island's water quality earned a grade of A- (86.8/100). The water generally meets EPA standards and is considered safe for consumption. The city ranks #80 out of 294 cities tested in Washington.
What contaminants are in Mercer Island's water?
Lead was measured at 6.3 ppb (90th percentile). No PFAS compounds were detected. 12 violations are on record.
How is Mercer Island's water quality grade calculated?
The grade is based on four factors: violation history (40%), lead and copper levels (25%), PFAS contamination (25%), and regulatory compliance (10%). The score is also adjusted based on how complete the available data is. See our methodology page for full details.
Do I need a water filter in Mercer Island?
While lead levels are within EPA limits, a filter adds extra protection. Based on current data, basic filtration should suffice for additional peace of mind.
Where does Mercer Island's water come from?
Mercer Island's water is sourced from Purchased surface water. The city has 2 water systems serving approximately 30,785 residents.
What health violations has Mercer Island's water system had?
Mercer Island has 1 health-based violation on record. The most recent violation was recorded in July 2011. Health-based violations mean the water exceeded EPA maximum contaminant levels (MCLs) for a regulated substance. 3 violations remain unresolved.
How does Mercer Island's water compare to other cities?
Mercer Island ranks #80 out of 294 cities in Washington (better than 73% of state cities) and #4425 out of 15744 cities nationally (72th percentile). The grade of A- reflects the combined assessment of violation history, lead and copper levels, PFAS contamination, and regulatory compliance.