Is Modesto, CA Tap Water Safe to Drink?
Graded D — but Strontium, Manganese and 2 more were detected above EPA limits. Here's what's in the water and how to remove it. What to do next ↓
49.9/100
waterverge.com Modesto, CA — Water Quality Report
Modesto's drinking water received a grade of D (49.9 out of 100), indicating poor water quality. The city's 18 water systems serve approximately 248,872 residents using purchased surface water.
Lead levels were measured at 12.0 ppb (90th percentile), which is within EPA limits but above recommended levels. UCMR 5 testing detected 8 PFAS compounds, with levels exceeding EPA maximum contaminant levels in the water supply.
The system has 149 violations on record, including 76 health-based violations. 14 remain unresolved.
What to know about Modesto's water
Modesto ranks #609 out of 694 cities in California for water quality, placing it among the lowest-rated 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.
Of particular concern: PFAS "forever chemical" levels exceed the 2024 EPA maximum contaminant levels. These synthetic compounds don't break down naturally and require specialized filtration such as reverse osmosis or granular activated carbon.
Hexavalent chromium (chromium-6) was detected at 7.00 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.
The system has seen 7 violations in the past five years, suggesting a pattern of compliance challenges that residents should monitor closely.
Water quality score
See methodology →Is Modesto, CA water safe to drink?
Modesto's drinking water has significant quality concerns based on EPA testing data. With a grade of D (49.9/100), the system has issues across multiple categories. A water filter is recommended for all residents. The city's 18 water systems serve approximately 248,872 residents using surface water (rivers, lakes, or reservoirs).
Recent water quality updates for Modesto
A timeline of significant water quality events, violations, and data updates.
PFAS levels exceed EPA maximum contaminant levels. Reverse osmosis or activated carbon filtration recommended.
Latest EPA compliance and testing data incorporated into Modesto's water quality assessment. Grade: D (49.9/100).
Contaminants: Lead and Copper Rule.
Contaminants: Lead and Copper Rule.
Contaminants: Combined Uranium.
Federal disaster declaration (FEMA DR-3592). Flood event — may have impacted local water infrastructure.
Key contaminant findings
Based on the most recent EPA sampling data for Modesto'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.
PFAS "forever chemicals" exceed EPA maximum contaminant levels. Reverse osmosis or granular activated carbon filtration strongly recommended.
The "Erin Brockovich" chemical. There is no federal MCL, but California has set a limit of 10 µg/L. Reverse osmosis filtration is effective at removing hexavalent chromium.
PFAS "forever chemicals" detected
UCMR 5 testing found 8 PFAS compounds in Modesto's water supply. PFAS are synthetic chemicals that persist indefinitely in the environment and the human body.
Violation history
Modesto's water system has 149 total violations on record, including 76 health-based violations. 14 remain unresolved. 7 violations were issued in the last 5 years.
Flood & environmental risk
Stanislaus County has experienced 8 federally declared disasters since 1964. 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 Tuolumne R A Modesto, Stanislaus R A Oakdale, Stanislaus R A Ripon.
Where does Modesto's water come from?
Modesto's drinking water comes from surface water (rivers, lakes, or reservoirs), supplied by 18 water systems serving approximately 248,872 people. Surface water sources are more susceptible to contamination from runoff, industrial discharge, and algal blooms, requiring extensive treatment. Nearby water bodies include Tuolumne R A Modesto (river), Stanislaus R A Oakdale (river), Stanislaus R A Ripon (river).
What Modesto residents can do
Recommended: Reverse osmosis system. This addresses the specific contaminants found in Modesto'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.
Modesto'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 Modesto
Industrial polluters nearby
Reported releases to surface water by facilities near Modesto, ranked by pounds discharged annually.
| Facility | Top chemical | To surface water (lbs/yr) | Distance |
|---|---|---|---|
CRYSTAL CREAMERY INC. MODESTO, CA95351 | — | — | 0.8 mi |
CEMEX MODESTO PLANT MODESTO, CA95354 | — | — | 3.3 mi |
FRITO LAY INC. MODESTO, CA95357 | — | — | 4.4 mi |
GALLO GLASS CO MODESTO, CA95354 | — | — | 1.6 mi |
BLUE DIAMOND GROWERS MODESTO, CA95356 | — | — | 6.4 mi |
Source: EPA Toxic Release Inventory (TRI) 2023
Superfund sites within 10 miles of Modesto
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.
- MODESTO GROUND WATER CONTAMINATION1.5 mi
- RIVERBANK ARMY AMMUNITION PLANT7.2 mi
Source: EPA Superfund National Priorities List
Flood & disaster history
Stanislaus County has experienced 8 federally declared disasters since 1964. Flooding and severe weather can compromise water treatment infrastructure and introduce contaminants into drinking water supplies.
Recommended water filters
Based on contaminants detected in Modesto'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. | 12.0 | 15 | ppb | Inorganic | Near Limit |
| 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. | 21.000 | HI | µg/L | PFAS | 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. | 0.004 | HI | µg/L | PFAS | 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. | 0.004 | HI | µg/L | PFAS | 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. | 0.006 | HI | µg/L | PFAS | 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. | 0.009 | HI | µg/L | PFAS | 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. | 0.009 | 0.004 | µg/L | PFAS | Over MCL |
| 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. | 0.026 | 0.004 | µg/L | PFAS | Over MCL |
| 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. | 0.007 | HI | µg/L | PFAS | 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 Modesto compares by contaminant
Explore where Modesto ranks among all California cities for specific contaminants.
Water source & infrastructure
Where Modesto's water comes from
Modesto'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 248,872 people through 18 water systems.
Water bodies near Modesto
Modesto is located near 3 notable water bodies. As a surface water system, these water bodies may directly influence the city's drinking water supply.
Water systems serving Modesto
| System Name | PWSID | Population | Source |
|---|---|---|---|
| MODESTO, CITY OF | CA5010010 | 218,771 | SWP |
| CITY OF MODESTO - SALIDA | CA5010005 | 14,537 | GW |
| CITY OF WATERFORD | CA5010006 | 8,788 | GW |
| CITY OF MODESTO - DEL RIO | CA5010029 | 1,327 | GW |
| CITY OF MODESTO - SOUTH TURLOCK | CA5010023 | 1,099 | GW |
| CITY OF MODESTO - GRAYSON | CA5010033 | 914 | GW |
| HILLSVIEW HOMES | CA5010007 | 887 | GW |
| RIVERDALE PARK TRACT CSD | CA5000019 | 610 | GW |
| WATERFORD - HICKMAN | CA5010026 | 597 | GW |
| BUENA VISTA MIGRANT CENTER | CA4400763 | 455 | GW |
| PARK HEIGHTS MUTUAL WATER CO | CA5000017 | 250 | GW |
| CITY OF MODESTO - WALNUT MANOR | CA5010031 | 175 | GW |
| CITY OF MODESTO - NORTH TURLOCK | CA5010034 | 172 | GW |
| CITY OF MODESTO - CENTRAL TURLOCK | CA5010035 | 119 | GWP |
| MORNINGSIDE MOBILEHOME PARK | CA5000054 | 67 | GW |
| COUNTRY WESTERN MHRV | CA5000080 | 55 | GW |
| RIVER ROAD MUTUAL WATER COMPANY | CA5000020 | 26 | GW |
| MODESTO IRRIGATION DISTRICT | CA5010038 | 23 | SW |
How Modesto compares
Full California rankings →Modesto's score of 49.9/100 is below the average of 57/100 among major California cities. It outscores 5 of 10 nearby cities.
Nearby cities
View California rankings →About Modesto, CA
Wikipedia →Modesto is the county seat of and the largest city in Stanislaus County, California, United States. With a population of 218,069 according to 2022 U.S. Census Bureau estimates, it is the 19th-most populous city in California.
Learn more about your water
Guides and resources related to Modesto's water quality findings.
Explore water quality across Stanislaus
Frequently asked questions
Is Modesto, CA tap water safe to drink?
Modesto's water quality earned a grade of D (49.9/100). Significant issues have been found. A water filter is strongly recommended. The city ranks #609 out of 694 cities tested in California.
What contaminants are in Modesto's water?
Lead was measured at 12.0 ppb (90th percentile). 8 PFAS compounds were detected. 149 violations are on record.
How is Modesto'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 Modesto?
While lead levels are within EPA limits, a filter adds extra protection. PFAS compounds exceed EPA limits — a reverse osmosis or activated carbon filter is recommended.
Where does Modesto's water come from?
Modesto's water is sourced from Purchased surface water. The city has 18 water systems serving approximately 248,872 residents.
What health violations has Modesto's water system had?
Modesto has 76 health-based violations on record. The most recent violation was recorded in July 2025. Health-based violations mean the water exceeded EPA maximum contaminant levels (MCLs) for a regulated substance. 14 violations remain unresolved.
Why does Modesto have so many PFAS compounds in its water?
8 different PFAS "forever chemical" compounds were detected in Modesto's water supply during UCMR 5 testing. PFAS contamination often originates from proximity to military installations (AFFF firefighting foam), airports, industrial manufacturing sites, or wastewater treatment facilities. Some levels exceed the 2024 EPA maximum contaminant levels — a reverse osmosis or NSF-certified activated carbon filter is strongly recommended.
How does Modesto's water compare to other cities?
Modesto ranks #609 out of 694 cities in California (better than 12% of state cities) and #13204 out of 15744 cities nationally (16th percentile). The grade of D reflects the combined assessment of violation history, lead and copper levels, PFAS contamination, and regulatory compliance.