waterverge.com Foster City, CA — Water Quality Report
Foster City's drinking water received a grade of A+ (97.9 out of 100), indicating excellent water quality. The city's 1 water system serves approximately 36,556 residents using purchased surface water.
Lead levels were measured at 0.0 ppb (90th percentile), well within EPA limits. PFAS testing under UCMR 5 found no detectable forever chemicals.
The system has 5 violations on record, including 2 health-based violations. All violations have been resolved.
What to know about Foster City's water
Foster City ranks #8 out of 694 cities in California for water quality, placing it one of the best 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 0.09 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 Foster City, CA water safe to drink?
Based on EPA testing data, Foster City's tap water is generally safe to drink. The water system earned a grade of A+ (97.9/100), meeting federal drinking water standards across key contaminant categories. The city's 1 water system serves approximately 36,556 residents using surface water (rivers, lakes, or reservoirs).
Recent water quality updates for Foster City
A timeline of significant water quality events, violations, and data updates.
Latest EPA compliance and testing data incorporated into Foster City's water quality assessment. Grade: A+ (97.9/100).
Federal disaster declaration (FEMA DR-3592). Flood event — may have impacted local water infrastructure.
Federal disaster declaration (FEMA DR-4683). Flood event — may have impacted local water infrastructure.
Contaminants: TTHM.
1 health-based. Contaminants: Coliform (TCR).
Contaminants: Lead and Copper Rule.
Key contaminant findings
Based on the most recent EPA sampling data for Foster City's water supply.
Well within EPA limits.
Violation history
Foster City's water system has 5 total violations on record, including 2 health-based violations. All violations have been resolved. 1 violation was issued in the last 5 years.
Flood & environmental risk
San Mateo County has experienced 9 federally declared disasters since 1982. 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 Pilarcitos C Ab Stone Dam Nr Hillsborough, Pilarcitos C Bl Stone Dam Nr Hillsborough, San Mateo C Ab Junction Box A Dam1 Nr Hillsborough, San Mateo C Bl Junction Box A Dam1 Nr Hillsborough, Lower Crystal Springs Res Nr San Mateo.
Where does Foster City's water come from?
Foster City's drinking water comes from surface water (rivers, lakes, or reservoirs), supplied by 1 water system serving approximately 36,556 people. Surface water sources are more susceptible to contamination from runoff, industrial discharge, and algal blooms, requiring extensive treatment. Nearby water bodies include Pilarcitos C Ab Stone Dam Nr Hillsborough (river), Pilarcitos C Bl Stone Dam Nr Hillsborough (river), San Mateo C Ab Junction Box A Dam1 Nr Hillsborough (river), San Mateo C Bl Junction Box A Dam1 Nr Hillsborough (river), Lower Crystal Springs Res Nr San Mateo (lake).
What Foster City residents can do
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.
Foster City'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 July 2026.
Top contaminants to know
View all ↓Forever chemicals overview
National PFAS report →Violation summary
Violations & advisories
Top industrial polluters within 10 miles of Foster City
Industrial polluters nearby
Reported releases to surface water by facilities near Foster City, ranked by pounds discharged annually.
Total reported releases to surface water: 3 lbs
| Facility | Top chemical | To surface water (lbs/yr) | Distance |
|---|---|---|---|
ROHM & HAAS CHEMICALS LLC HAYWARD, CA94545 | Zinc compounds | 3 | 8.1 mi |
GRANITE ROCK CO REDWOOD CITY REDWOOD CITY, CA94063 | Barium | 0 | 5.3 mi |
GARRATT-CALLAHAN CO BURLINGAME BURLINGAME, CA94010 | — | — | 7.3 mi |
CSBIO MENLO PARK, CA94025 | — | — | 8.3 mi |
UNIVAR SOLUTIONS USA REDWOOD CITY, CA94063 | — | — | 4.8 mi |
Source: EPA Toxic Release Inventory (TRI) 2023
Flood & disaster history
San Mateo County has experienced 9 federally declared disasters since 1982. 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 |
|---|---|---|---|---|---|
| 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. | 0.0 | 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 Foster City compares by contaminant
Explore where Foster City ranks among all California cities for specific contaminants.
Water source & infrastructure
Where Foster City's water comes from
Foster City'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 36,556 people through 1 water system.
Water bodies near Foster City
Foster City 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 Foster City
| System Name | PWSID | Population | Source |
|---|---|---|---|
| ESTERO MUNICIPAL IMPROVEMENT DISTRICT | CA4110021 | 36,556 | SWP |
How Foster City compares
Full California rankings →Foster City's score of 97.9/100 is above the average of 57/100 among major California cities. It outscores 10 of 10 nearby cities.
Nearby cities
View California rankings →ZIP codes served by Foster City
The water system serving Foster City covers 1 ZIP code. Select any ZIP to see which water systems serve that area.
About Foster City, CA
Wikipedia →Foster City is a master-planned city located in San Mateo County, California, United States. Foster City is sometimes considered to be part of Silicon Valley for its local industry and its proximity to Silicon Valley cities. There are many notable companies headquartered in Foster City, such as Gilead Sciences, Zoox, and Replit. Visa and Sledgehammer Games were formerly headquartered in Foster City.
Learn more about your water
Guides and resources related to Foster City's water quality findings.
Explore water quality across San Mateo
Frequently asked questions
Is Foster City, CA tap water safe to drink?
Foster City's water quality earned a grade of A+ (97.9/100). The water generally meets EPA standards and is considered safe for consumption. The city ranks #8 out of 694 cities tested in California.
What contaminants are in Foster City's water?
Lead was measured at 0.0 ppb (90th percentile). No PFAS compounds were detected. 5 violations are on record.
How is Foster City'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 Foster City?
Based on current data, basic filtration should suffice for additional peace of mind.
Where does Foster City's water come from?
Foster City's water is sourced from Purchased surface water. The city has 1 water system serving approximately 36,556 residents.
What health violations has Foster City's water system had?
Foster City has 2 health-based violations on record. The most recent violation was recorded in July 2022. Health-based violations mean the water exceeded EPA maximum contaminant levels (MCLs) for a regulated substance. All health violations have been resolved.
How does Foster City's water compare to other cities?
Foster City ranks #8 out of 694 cities in California (better than 99% of state cities) and #55 out of 15744 cities nationally (100th percentile). The grade of A+ reflects the combined assessment of violation history, lead and copper levels, PFAS contamination, and regulatory compliance.