Is Mountlake Terrace, WA Tap Water Safe to Drink?
Graded B+, with 8 unresolved violations on record. See what was cited — and what it means for your tap. What to do next ↓
82.4/100
waterverge.com Mountlake Terrace, WA — Water Quality Report
Mountlake Terrace's drinking water received a grade of B+ (82.4 out of 100), indicating good water quality. The city's 1 water system serves approximately 26,402 residents using purchased surface water.
Lead data is not currently available for this system. PFAS testing under UCMR 5 found no detectable forever chemicals.
The system has 12 violations on record, including 0 health-based violations. 8 remain unresolved.
What to know about Mountlake Terrace's water
Mountlake Terrace ranks #122 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.
Haloacetic acid (HAA5) levels were elevated at 36.0 µg/L in UCMR 4 testing, though below the 60 µg/L EPA limit. Activated carbon filtration can help reduce these disinfection byproducts.
Hexavalent chromium (chromium-6) was detected at 0.31 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.
Water quality score
See methodology →Is Mountlake Terrace, WA water safe to drink?
Mountlake Terrace's drinking water has significant quality concerns based on EPA testing data. With a grade of B+ (82.4/100), the system has issues across multiple categories. A water filter is recommended for all residents. The city's 1 water system serves approximately 26,402 residents using surface water (rivers, lakes, or reservoirs).
Recent water quality updates for Mountlake Terrace
A timeline of significant water quality events, violations, and data updates.
Latest EPA compliance and testing data incorporated into Mountlake Terrace's water quality assessment. Grade: B+ (82.4/100).
Federal disaster declaration (FEMA DR-3629). Flood event — may have impacted local water infrastructure.
Contaminants: Consumer Confidence Rule.
Federal disaster declaration (FEMA DR-4539). Flood event — may have impacted local water infrastructure.
Contaminants: Total Haloacetic Acids (HAA5), TTHM.
Contaminants: TTHM.
Violation history
Mountlake Terrace's water system has 12 total violations on record, including 0 health-based violations. 8 remain unresolved. 1 violation was issued in the last 5 years.
Flood & environmental risk
Snohomish County has experienced 10 federally declared disasters since 1979. Flooding and severe storms can overwhelm water treatment plants, cause sewage overflows, and introduce agricultural runoff, bacteria, and sediment into drinking water supplies.
Where does Mountlake Terrace's water come from?
Mountlake Terrace's drinking water comes from surface water (rivers, lakes, or reservoirs), supplied by 1 water system serving approximately 26,402 people. Surface water sources are more susceptible to contamination from runoff, industrial discharge, and algal blooms, requiring extensive treatment.
What Mountlake Terrace residents can do
Recommended: NSF-certified water filter. This addresses the specific contaminants found in Mountlake Terrace'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.
Mountlake Terrace'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 Mountlake Terrace
Industrial polluters nearby
Reported releases to surface water by facilities near Mountlake Terrace, ranked by pounds discharged annually.
Total reported releases to surface water: 13 lbs
| Facility | Top chemical | To surface water (lbs/yr) | Distance |
|---|---|---|---|
BOEING COMMERCIAL AIRPLANES - EVERETT EVERETT, WA98204 | Copper | 13 | 8.8 mi |
ROMAC INDUSTRIES INC BOTHELL, WA98021 | — | — | 4.5 mi |
CEPHEID - BOTHELL BOTHELL, WA98021 | — | — | 4.3 mi |
TR INTERNATIONAL TRADING CO DBA CATALYNT SOLUTIONS EDMONDS, WA98020 | — | — | 3.1 mi |
WESTERN PNEUMATIC TUBE CO LLC KIRKLAND, WA98033 | — | — | 10.0 mi |
Source: EPA Toxic Release Inventory (TRI) 2023
Flood & disaster history
Snohomish County has experienced 10 federally declared disasters since 1979. Flooding and severe weather can compromise water treatment infrastructure and introduce contaminants into drinking water supplies.
Full contaminants report
| Contaminant | Detected Level | EPA Limit | Unit | Category | Status |
|---|---|---|---|---|---|
| 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 |
See how Mountlake Terrace compares by contaminant
Explore where Mountlake Terrace ranks among all Washington cities for specific contaminants.
Water source & infrastructure
Where Mountlake Terrace's water comes from
Mountlake Terrace'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 26,402 people through 1 water system.
Water systems serving Mountlake Terrace
| System Name | PWSID | Population | Source |
|---|---|---|---|
| MOUNTLAKE TERRACE CITY OF | WA5357250 | 26,402 | SWP |
How Mountlake Terrace compares
Full Washington rankings →Mountlake Terrace's score of 82.4/100 is above the average of 53/100 among major Washington cities. It outscores 9 of 10 nearby cities.
Nearby cities
View Washington rankings →About Mountlake Terrace, WA
Learn more about your water
Guides and resources related to Mountlake Terrace's water quality findings.
Explore water quality across Snohomish
Frequently asked questions
Is Mountlake Terrace, WA tap water safe to drink?
Mountlake Terrace's water quality earned a grade of B+ (82.4/100). The water generally meets EPA standards and is considered safe for consumption. The city ranks #122 out of 294 cities tested in Washington.
What contaminants are in Mountlake Terrace's water?
No PFAS compounds were detected. 12 violations are on record.
How is Mountlake Terrace'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 Mountlake Terrace?
Based on current data, basic filtration should suffice for additional peace of mind.
Where does Mountlake Terrace's water come from?
Mountlake Terrace's water is sourced from Purchased surface water. The city has 1 water system serving approximately 26,402 residents.
How does Mountlake Terrace's water compare to other cities?
Mountlake Terrace ranks #122 out of 294 cities in Washington (better than 59% of state cities) and #6946 out of 15744 cities nationally (56th percentile). The grade of B+ reflects the combined assessment of violation history, lead and copper levels, PFAS contamination, and regulatory compliance.