Tap Water Quality Report
Tap water quality in Modesto, California
Tap water in Modesto, California receives a grade of F (47/100) from TapWaterSafety.org. It's served by MODESTO, CITY OF. The most significant water quality concerns are: PFAS contamination; Perfluorohexane sulfonate (PFHXS) significantly above health guideline; Arsenic significantly above health guideline; Haloacetic acids (HAA5) significantly above health guideline. Data sources: EPA SDWIS, EPA ECHO, EWG Tap Water Database.
What's in Modesto's tap water
Top water quality concerns identified by the EPA and Environmental Working Group across the utility serving Modesto.
PFAS contamination
Severe concernPerfluorooctane sulfonate (PFOS), Perfluorooctanoic acid (PFOA) detected. PFAS are persistent chemicals linked to cancer and immune effects with no known safe exposure threshold.
Perfluorohexane sulfonate (PFHXS) significantly above health guideline
Moderate concernPerfluorohexane sulfonate (PFHXS) detected at 0.493 ppt, 493x above the EWG health guideline of 0.001 ppt.
Arsenic significantly above health guideline
Moderate concernArsenic detected at 1.73 ppb, 434x above the EWG health guideline of 0.004 ppb.
Haloacetic acids (HAA5) significantly above health guideline
Moderate concernHaloacetic acids (HAA5) detected at 36.2 ppb, 362x above the EWG health guideline of 0.1 ppb.
EPA compliance record
Official U.S. EPA records for MODESTO, CITY OF (system ID CA5010010) for the last 3 years. Checked 2026-10-07.
Source: U.S. EPA Enforcement and Compliance History Online (ECHO), from the Safe Drinking Water Information System. See EPA's full report.
Recommended filters for Modesto
Filters matched to the specific contaminants in Modesto's water supply.
Filter certified for PFOA/PFOS (NSF/ANSI 53 or 58)
$180-$750Reverse osmosis and some carbon block filters reduce PFAS. Look for certification to NSF/ANSI 53 or 58 for PFOA/PFOS.
Reverse osmosis certified for arsenic (NSF/ANSI 58)
$429-$599Reverse osmosis certified under NSF/ANSI 58 for arsenic is the most reliable home option.
Carbon filter certified for VOCs (NSF/ANSI 53)
$180-$599Activated carbon is effective for disinfection byproducts. Look for NSF/ANSI 53 VOC reduction.
Disclosure: TapWaterSafety earns a commission from purchases made through these links. This does not influence our scoring methodology or filter selection.
All contaminants detected in Modesto's tap water
Every contaminant identified, compared side-by-side against US EPA legal limits, the EU Drinking Water Directive (2020/2184), WHO Guidelines, and California's Public Health Goal. Why we show multiple standards →
| Contaminant | Detected | EWG US health-based |
EPA US legal |
EU DWD Europe |
WHO global |
CA PHG strictest US |
Tested sample year |
Status |
|---|---|---|---|---|---|---|---|---|
| Perfluorohexane sulfonate (PFHXS) PFAS |
0.493 ppt | 0.001 | 10.0 | — | — | — | — | 493× over |
| Arsenic Heavy metal |
1.73 ppb | 0.004 | 10.0 | 10 | 10 | 0.004 | — | 434× over |
| Haloacetic acids (HAA5) Disinfection byproduct |
36.2 ppb | 0.1 | 60.0 | 60 | — | — | — | 362× over |
| Haloacetic acids (HAA9) Disinfection byproduct |
20.1 ppb | 0.06 | — | — | — | — | — | 335× over |
| Total trihalomethanes (TTHMs) Disinfection byproduct |
44.8 ppb | 0.15 | 80.0 | 100 | — | — | — | 299× over |
| Trichloroacetic acid Disinfection byproduct |
13.5 ppb | 0.1 | — | — | — | — | — | 135× over |
| Chromium (hexavalent) Heavy metal |
2.58 ppb | 0.02 | — | — | — | — | — | 129× over |
| Chloroform Disinfection byproduct |
41.0 ppb | 0.4 | — | — | — | — | — | 103× over |
| Dichloroacetic acid Disinfection byproduct |
14.3 ppb | 0.2 | — | — | — | — | — | 72× over |
| Bromodichloromethane Disinfection byproduct |
2.33 ppb | 0.06 | — | — | — | — | — | 39× over |
| Nitrate Inorganic |
5.12 ppm | 0.14 | 10.0 | 11.3 | 11.3 | 10 | — | 37× over |
| Uranium Radiological |
6.32 pCi/L | 0.43 | 20.0 | 30 | 30 | 0.43 | — | 15× over |
| Dibromochloromethane Disinfection byproduct |
1.05 ppb | 0.1 | — | — | — | — | — | 10× over |
| Dibromoacetic acid Disinfection byproduct |
0.148 ppb | 0.03 | — | — | — | — | — | 4.9× over |
| Perfluorooctanoic acid (PFOA) PFAS |
0.397 ppt | 0.09 | 4.0 | 100 | 100 | 0.007 | — | 4.4× over |
| Tetrachloroethylene (perchloroethylene) Volatile organic compound |
0.228 ppb | 0.06 | 5.0 | — | — | — | — | 3.8× over |
| Perfluorooctane sulfonate (PFOS) PFAS |
0.966 ppt | 0.3 | 4.0 | 100 | 100 | 1 | — | 3.2× over |
| Bromate* Disinfection byproduct |
0.268 ppb | 0.1 | 10.0 | 10 | 10 | 0.1 | — | 2.7× over |
| 1,2,3-Trichloropropane Other |
0.000935 ppb | 0.0007 | — | — | — | — | — | 1.3× over |
| 1,2-Dibromo-3-chloropropane (DBCP) Other |
0.00183 ppb | 0.0017 | 0.2 | — | — | — | — | 1.1× over |
| Vanadium Other |
16.9 ppb | 21.0 | — | — | — | — | — | Below guideline |
| Bromoform Disinfection byproduct |
0.371 ppb | 0.5 | — | — | — | — | — | Below guideline |
| Chlorate Disinfection byproduct |
146.3 ppb | 210.0 | — | — | — | — | — | Below guideline |
| Trichloroethylene Volatile organic compound |
0.0489 ppb | 0.4 | 5.0 | 10 | 20 | 1.7 | — | Below guideline |
| Barium Heavy metal |
71.5 ppb | 700.0 | 2000.0 | — | 1300 | 2000 | — | Below guideline |
| Molybdenum Other |
1.25 ppb | 40.0 | — | — | — | — | — | Below guideline |
| 1,4-Dioxane Semi-volatile organic compound |
0.00755 ppb | 0.35 | — | — | 50 | 1 | — | Below guideline |
| Manganese Heavy metal |
0.885 ppb | 100.0 | — | 50 | 80 | — | — | Below guideline |
| Monochloroacetic acid Disinfection byproduct |
0.0989 ppb | 53.0 | — | — | — | — | — | Below guideline |
| Aluminum Heavy metal |
0.943 ppb | 600.0 | — | 200 | — | 600 | — | Below guideline |
| Strontium Radiological |
0.584 ppb | 1500.0 | — | — | — | — | — | Below guideline |
| Perfluoropentanoic Acid (PFPeA) PFAS |
0.321 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Perfluorohexanoic Acid (PFHxA) PFAS |
0.193 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| 1,1-Dichloroethane Volatile organic compound |
0.00025 ppb | 3.0 | — | — | — | — | — | Below guideline |
| Perfluorobutane sulfonate (PFBS) PFAS |
0.157 ppt | 2000.0 | — | — | — | — | — | Below guideline |
| Perfluorobutanoic Acid (PFBA) PFAS |
0.052 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Perfluoroheptanoic acid (PFHPA) PFAS |
0.02 ppt | 1000.0 | — | — | — | — | — | Below guideline |
| Xylenes (total) Volatile organic compound |
0.00349 ppb | 1800.0 | 10000.0 | — | — | — | — | Below guideline |
| Bromide* Other |
144.9 ppb | — | — | — | — | — | — | Below guideline |
| Chlorodifluoromethane Other |
0.124 ppb | — | — | — | — | — | — | Below guideline |
| Dichlorodifluoromethane Other |
0.112 ppb | — | — | — | — | — | — | Below guideline |
| Fluoride Inorganic |
0.0258 ppm | — | 4.0 | 1.5 | 1.5 | — | — | Below guideline |
| Lithium Other |
2.03 ppb | — | — | — | — | — | — | Below guideline |
All values in the unit of the detected level. Red cells indicate the detected level exceeds that standard. Some contaminants have limits in some jurisdictions but not others (shown as —). The "Tested" column shows the year each contaminant sample was collected.
Sources: US EPA, EU Drinking Water Directive 2020/2184, WHO Guidelines, California OEHHA PHGs, EWG Tap Water Database.
Treatment plant contact info
For service issues, water quality concerns, or to request a Consumer Confidence Report from MODESTO, CITY OF.